The primary objective of this study was to determine whether cadmium (Cd) exposures during embryonic and larval development alter the reproductive performance, reproductive physiology, and sex ratio of fathead minnows (Pimephales promelas). Embryonic exposures were conducted by exposing adult female fathead minnows to 0, 25, or 100 microg/L Cd for 8 d prior to breeding. Larval exposures were conducted by exposing the larvae to waterborne Cd at 0, 12.5, 25, or 50 microg/L from 8 to 29 d posthatch (the time period associated with female sexual differentiation). Minnows from each exposure period were raised to maturity, at which time their reproductive success, secondary sexual characteristics, gonadosomatic index (GSI), plasma 11-ketotestosterone (11-KT) concentrations, and sex ratios were assessed. Results from the embryonic study reveal that Cd exposures alter the secondary sexual characteristics of male fathead minnows but do not alter reproductive performance, GSI, 11-KT concentrations, or sex ratios. Larval exposures, during the period of female sexual differentiation, significantly reduce the frequency of adult spawning and increase clutch size but do not alter fecundity, secondary sexual characteristics, GSI, or 11-KT. Subtle alterations in sex ratio were observed, indicating that larval Cd exposures may increase the proportion of females in an exposed population.