Most research on the relationship between personality and overall job performance assumes linearity and homoscedasticity. This study investigated the prevalence and nature of nonlinearities and heteroscedasticies in relationships between conscientiousness and supervisory ratings of overall job performance across five independent samples using both concurrent (k = 4) and predictive (k = 1) designs. Hierarchical polynomial regression analyses found evidence of robust linear effects but no evidence of statistically significant quadratic or cubic effects. A statistically and practically significant heteroscedastic effect was found in only one sample such that lower errors of prediction were evidenced in the ends in comparison to the middle of the bivariate distribution. Implications for the use of conscientiousness in personnel selection are suggested. Limitations of the current study and directions for future research are noted.