We studied clutch size, hatching and fledging success, and time necessary for chick Kelp Gulls (Larus dominicanus) to leave the nest throughout two breeding seasons (2004 and 2005) on Guararitama Island, São Paulo, Brazil. We followed 93 nests in 2004 and 97 nests in 2005. The average (± SD) clutch size was 2.09 ± 0.64 in 2004 and 1.93 ± 0.59 in 2005. Hatching success was 74% in 2004 and 53% in 2005, and fledging success was 54% in 2004 and 58% in 2005. Chicks grew quickly, following the linear equation y(t)  =  61g 17.03g × age (in days), and began to fly at 40 days.