Objective: The current study examined whether the arithmetical calculation skills of children, adolescents, and young adults with isolated cleft of the lip and/or palate (iCL/P) differ significantly from unaffected control participants. Comparisons of potential neuropsychological predictors of arithmetical calculation were also conducted to determine whether these variables differ significantly for participants with iCL/P. Method: Participants (N = 176; 93 iCL/P and 83 Control) ranged in age from 7 to 26 years old. A standardized battery of achievement and neuropsychological skills was administered. Between group differences on math achievement was assessed through a univariate analysis of covariance. Relationships between neuropsychological measures and math achievement were analyzed separately for participants with iCL/P and controls through hierarchical linear regressions. Results: Arithmetical calculation was significantly lower for the iCL/P group. Rapid naming, sustained attention, and visual-spatial organization were significant predictors for the iCL/P group; rapid naming was the lone variable that was significantly more predictive of arithmetical calculation for the iCL/P group than for control participants. Conclusions: These results suggest that inefficient verbal label retrieval related to short-term memory (STM) deficits underlie the calculation difficulties of individuals with iCL/P. These findings have implications for approaches to remediation, as well as future research.