The queen conch (Strombus gigas) is a large economically important gastropod that has been severely depleted throughout much of the Caribbean region. The species has determinate growth and reaches maximum shell length before sexual maturation; thereafter the shell grows only in thickness. In this study, queen conch were collected in the Exuma Cays, Bahamas, to evaluate maturity with respect to shell length (SL) (170–255 mm) and shell lip thickness (LT) (2–42 mm). Soft tissue weight and gonad weight increased with SL, but these same variables, along with the gonadosomatic index (gonad weight/soft tissue weight), all had dome-shaped distributions with LT and decreased slightly with LT > 22 mm. This indicates some loss of fecundity with age; however, no loss of reproductive capability was evident in histological data. Gonad maturity lagged substantially behind first formation of the shell lip. Minimum LT for reproductive maturity was 12 mm for females and 9 mm for males, and 50% maturity for the population was achieved at 26 mm LT for females and 24 mm LT for males, higher than previous estimates. A review of fishing regulations indicates that immature queen conch are being harvested legally in most Caribbean nations, providing at least a partial explanation for widespread depletion. While relationships between shell lip thickness, age, and maturity vary geographically, sustainable management of queen conch will require a minimum shell lip thickness for harvest no less than 15 mm, along with other urgently needed management measures.