The reproductive biology of the Panama brief squid was evaluated using reproductive indicators, and histological and histochemical analyses. A total of 2,460 squid were analyzed, which were captured during 15 exploratory fishing surveys in the Gulf of California during 2003 to 2006 and 2008. Of the total sample, 61% were female, 15% were male, and the rest were undifferentiated. Based on the frequency of the gonad developmental stages, the largest number of mature females was identified in February and October, whereas mature males were found in April and August. This result coincided with the gonadosomatic index. According to the histological analyses, we characterized 4 stages of oogenesis: previtellogenesis, vitellogenesis, postvitellogenesis with mature oocytes, and postspawning. We also characterized 6 substages of oocyte and 2 structural indicators of spawning: oogonia (Po0), previtellogenic oocyte primary (Pol), previtellogenic oocyte secondary (Po2), vitellogenic primary oocyte (Vol), secondary vitellogenic oocyte (Vo2), postvitellogenic oocyte (Pvo), postovulatory follicles, and atresia. Oocyte size among types showed significant differences (P < 0.05). The presence of postovulatory follicles, and oocytes of different sizes and various developmental stages throughout the study period indicates that the Panama brief squid has a synchronous ovarian development with multiple spawning. The size at first maturity (L50) indicates that males (mantle length, 51 mm) mature at lengths shorter than females (mantle length, 85 mm).