Pristimantis aff. fenestratus is a common species in non-flooded forests of central Amazonia, Brazil. Herein, we show the reproductive pattern and data on population structure of this species from two sites, using standardized sample methods (visual and auditory surveys), during three rainy seasons. The higher number of males in calling activity was detected in the beginning of the rainy season. However, sporadic male calls were also heard in the dry season. Females were significantly larger than males, and males captured at the end of the rainy season were larger than those captured in other periods. Females with eggs visible through the abdominal wall were found in all samplings at one site, but a larger number of juveniles were found at the end of the rainy season. The size of juveniles was variable and the smallest individuals were found at the end of the rainy season. According to nocturnal visual surveys males were significantly more abundant than females (1.9:1 adult sex ratio). According to data collected on gravid female occurrence, juvenile number variation, and presence of calling males, we suggest that P. aff. fenestratus reproduces during the rainy season showing marked seasonality.