We describe growth, longevity, sex ratio, reproductive period, and recruitment of Aegla paulensis from Jaraguá State Park, São Paulo, Brazil (23°27′27.9″S; 46°45′32.3″W). The population was sampled monthly (September 2007 through August 2009) with the aid of traps. Over five thousand individuals were captured, sexed, measured (carapace length  =  CL) and inspected for reproductive traits (females only), and then released back to the sampling site. The pattern of the reproductive cycle was strongly seasonal (austral mid autumn through late winter), with a single recruitment pulse per year. The obtained von Bertalanffy growth equations were CL  =  21.25[1-e^{−0.041(t 1.250)}] and CL  =  16.52[1-e^{−0.049(t 1.823)}] for males and females, respectively. Males (mean CL ± SD  =  11.86 ± 2.79 mm) attain larger sizes than females (mean CL ± SD  =  10.84 ± 2.36 mm). Aegla paulensis reproduces twice during an estimated life span of 40.2 months for females and 33.9 months for males. Temporal variation of sex ratio showed a distinctive pattern characterized by a sequence of three distinct periods that repeated from one year to another, and which suggested that a behavioral component influence the proportion of sex in adult specimens sampled with traps during reproductive and non-reproductive periods.