Background: The Tolosa Hunt syndrome is characterized by ophthalmoplegia with unilateral severe retroorbital pain associated to a granulomatous inflammatory process occupying the cavernous sinus or the superior orbital fissure. The etiol ogy is unknown and diagnosis is based upon a clinical response to steroid treatm ent and exclusion of neoplasm, trauma, aneurysms, infectious, and inflammatory d iseases. Case description.A 43 year old man was admitted because of a 1 week history of acute onset left sided retroorbital pain, followed by left sixth cra nial nerve palsy. Magnetic resonance imaging was normal and Tolosa Hunt syndrom e was suspected. Steroid treatment controlled pain with recovery of ophthalmople gia. Four months later, when a good response to treatment was still present, bra in magnetic resonance imaging revealed a lesion enlarging the left cavernous sin us, isointense with the gray matter on T1 weighted sequences, hypointense on T2 weighted images, and with homogeneous enhancement after gadolinium injection. Two months later, ocular pain and sixth cranial nerve palsy recurred and new bra in magnetic resonance imaging showed an extension of the tissue occupying the le ft cavernous sinus, over the sella, to the right cavernous sinus, making possibl e an endoscopic transphenoidal biopsy. Results. Histopathological study revealed a granulomatous aspecific inflammation containing actinomycetes colonies. The p atient was treated with intravenous penicillin G followed by amoxicillin per os, with improvement of pain and ophthalmoplegia. A control magnetic resonance imag ing 1 month after therapy showed a consistent reduction of the enlarged cavernou s sinus, and 3 months later neurological examination and brain magnetic resonanc e imaging were completely normal. Conclusions. The present case suggests that th e International Classification of Headache Disorders (2nd edition) definition of Tolosa Hunt syndrome does not reflect the complexity of the syndrome and that some cases of secondary painful ophthalmoplegias can fit the criteria for the pr imary form. Since the biopsy can only rarely be performed, we agree with other a uthors that clinical and radiological follow up should be performed for at least 2 years. Moreover, we propose that in patients with painful ophthalmoplegia hav ing transient response to steroid therapy, a trial with antibiotic therapy shoul d be taken into account. Background: The Tolosa Hunt syndrome is characterized by ophthalmoplegia with unilateral severe retroorbital pain associated to a granulomatous inflammatory process occupying the cavernous sinus or the superior orbital fissure. The etiology is unknown and diagnosis is based upon a clinical response to steroid treatm ent and exclusion of neoplasm, trauma, aneurysms, infectious, and inflammatory d iseases. Case description. A 43 year old man was admitted because of a 1 week history of acute onset left side retroorbital pain, followed by left sixth cra nial nerve palsy. was normal and Tolosa Hunt syndrom e was suspected. Steroid treatment controlled pain with recovery of ophthalmople gia. Four months later, when a good response to treatment was still present, bra in magnetic resonance imaging revealed a lesion enlarging the left cavernous sin us, isointense with the gray matter on T1 weighted sequences, hypointense on T2 weighted images, and with homogeneous en hancement after gadolinium injection. Two months later, ocular pain and sixth cranial nerve palsy recurred and new bra in magnetic resonance imaging showed an extension of the tissue occupying the le ft cavernous sinus, over the sella, to the right cavernous sinus, making possibl e An endoscopic transphenoidal biopsy. Results. Histopathological study revealed a granulomatous aspecific inflammation containing actinomycetes colonies. The p atient was treated with intravenous penicillin G followed by amoxicillin per os, with improvement of pain and ophthalmoplegia. A control magnetic resonance imag ing 1 month after therapy showed a consistent reduction of the enlarged cavernou s sinus, and 3 months later neurological examination and brain magnetic resonance imaging were completely normal. Conclusions. The present case suggests that th e International Classification of Headache Disorders (2nd edition) definition of Tolosa Hunt syndrome does not reflect the complexity of the syndrome andthat the cases of secondary painful ophthalmoplegias can fit the criteria for the pr imary form. we agree with other a uthors that clinical and radiological follow up should be performed at least 2 years. propose that in patients with painful ophthalmoplegia hav ing transient response to steroid therapy, a trial with antibiotic therapy shoul d be taken into account.