This study evaluated the clinical performance of a polyacid-modified resin composite, Dyract AP (De Trey/Dentsply), under different conditioning methods in primary teeth. Eighty-one box-shaped cavity preparations (three restorations per patient) on the mesial or distal surfaces of primary first or second molars were prepared in 27 patients. The cavity preparations were either non pre-treated or pre-treated with 36% phosphoric acid or NRC (De Trey/Dentsply). The teeth were restored with Prime & Bond NT (De Trey/Dentsply) and Dyract AP. The restorations were evaluated at baseline and 6, 12 and 18-month recalls according to the modified Ryge criteria by two calibrated operators. The data obtained from the clinical assessment of all restorations were subjected to statistical analysis by chi-square-tests at a 0.05 level of significance. The ratings of each criteria were compared among each evaluation period between treatment groups. Statistical analysis revealed no significant difference among each evaluation period between groups in regard to color match, marginal discoloration, marginal adaptation, secondary caries, surface texture, anatomic form and retention.