We report herein the use of p-dodecylbenzenesulfonic acid (DBSA) as a catalyst for a one-pot Biginelli reaction to afford 3,4-dihydropyrimidinone derivatives in good to excellent yields. This reaction proceeds efficiently in water and under solvent free conditions. Comparisons of results indicate that although the yields are high and comparable for both methods, the reaction times are considerably shorter under solvent free conditions.