This study evaluated and compared the fracture toughness of compomers and composites. Three compomer (Compoglass F [CG], Vivadent; F2000 [FT], 3M-ESPE; Dyract Posterior [DP], Dentsply) and three composite (Tetric Ceram [TC], Vivadent; Z250 [ZT], 3M-ESPE; Esthet X [EX], Dentsply) restoratives were selected for the study. Single-edged notched specimens (25 x 2 x 2 mm) were fabricated according to manufacturers' instructions and conditioned in distilled water at 37 degrees C for one week prior to testing. Seven specimens were made for each material. The specimens were loaded to failure using an Instron microtester with a crosshead speed of 0.5 mm/minute. Data were subjected to ANOVA/Scheffe's test and Independent Samples T-test at significance level 0.05. The mean fracture toughness (K(IC)) ranged from 0.97 to 1.23 MPam 1/2 for compomers and 1.75 to 1.92 MPam 1/2 for composites. The fracture toughness of compomers was significantly lower than their composite counterparts. No significant difference in K(IC) values was observed among the different composites. When the compomers were compared, FT had significantly higher fracture toughness than DP and CG. In view of their poorer resistance to crack propagation, compomers are not recommended for use in stress-bearing areas.