OBJECTIVE The purpose of this prospective study was to compare light-cured calcium hydroxide (Ca(OH)2) with diluted formocresol (FC) for its success as a primary molar pulpotomy medicament METHODS Selection criteria included at least 2 matching, asymptomatic, contralateral primary molars requiring vital pulpotomies. Matched teeth in each patient were randomized to receive either Ca(OH)2 or FC as a pulpotomy medicament. All teeth were restored with prefabricated metal crowns. Twenty patients (34 pairs of teeth) were followed clinically and radiographically for > or =1 year. Two blinded, standardized, and calibrated examiners evaluated and scored each radiograph for signs of pathology, based upon a modified scale previously proposed. RESULTS Findings were grouped in: (a) 0 - 6; (b) 7 - 12; and (c) 13 - 24 month intervals. Radiographic scoring favored the FC group of the 7- to 12- and 13- to 24-month intervals (P<.05). Clinical success was similar for Ca(OH)2 (94%) and FC (97%) at 12 months or less. Beyond 12 months, clinical success varied more (Ca(OH)2=84%, FC=97%), but not significantly (P=.08). Combined success rates were lower for Ca(OH)2 (56%) than FC (94%). CONCLUSIONS Light-cured calcium hydroxide does not appear to be a viable alternative to diluted formocresol as a pulpotomy agent.