The ruffe Gymnocephalus cernuus L. is an introduced species in Italy. In order to assess the impact of exotic species on native fish communities, the ecology and biology of intruders need to be thoroughly investigated. The aim of this study was to analyse the growth and reproductive biology of the ruffe population in Lake Piediluco. From June 1999 to March 2002, and between July 2004 and May 2005, 1 330 specimens belonging to seven age-classes were captured. Sex was determined in 385 individuals: 327 females and 58 males. The SL-TL relationship for the whole sample was TL = 0.923 + 1.075SL. The SL-W relationship was W = 0.0154 SL3.102 for females and W = 0.0157 SL3.106 for males. The parameters of the von Bertalanffy growth curve for length using back-calculated SL were L∞ = 218.29 mm, k = 0.27 y -1, t0 = -0.61 for females and L∞ = 161.54 mm, k = 0.32 y-1, t0 = -0.70 for males. The results showed that in Lake Piediluco ruffe grow as fast as in their original environments. Seasonal growth and back-calculation showed the possible existence of differential mortality prejudicial to small specimens. Moreover, growth analysis revealed marked sexual dimorphism in growth in the Lake Piediluco population. Sexual maturation occurred in both sexes at the end of the first year of life. Reproduction occurred mostly in May and June. The mean diameter of eggs was 1.12 mm. The mean number of eggs produced by each female was 11 961, and increased with the size of the specimens; with regard to relative fecundity, an average value of 239 eggs g-1 was observed. This analysis reveals some important biological characteristics of the ruffe that were not previously well known with regard to the Italian population of the species.