The general features of testes change with reproductive maturity and in many species of reptiles show a seasonal pattern reflected in macroscopic and microscopic gonadal changes. In previous studies the sexual maturity and reproductive cycle of Boa constrictor occidentalis (Boidae, Appendix I of CITES, 1997) have been determined by testes and epididymis macroscopic differences using ultrasound scanning on live individuals. In this study, the gametogenic activity is studied histologically and the correspondence with previous studies analysed. Our results corroborate the age classification based on morphological features and support the reproductive cycle described for B. c. occidentalis based on live individuals.