We described two members in a family with gastrointestinal stromal tumors (GISTs) without cutaneous hyperpigmentation. The patients were father and son who did not have cutaneous hyperpigmentation.Histological examination showed that these tumors were GISTs expressing CD34 and CD117. Tumor DNA extracted from paraffin-embedded specimens revealed somatic mutation with a deletion mutation at different codons in exon 11 of c-kit gene after direct sequencing analysis.No germline mutation was detected in DNA extracted from peripheral leukocytes obtained from the father and son. We propose that GISTs could be caused by sporadic somatic mutation in a family without germline mutation and hyperpigmentation.