The aim of this study was to compare growth, gonadal structure and red blood cell sizes of triploid and diploid brown trout (Salmo trutta fario). Triploidy was induced by providing a heat shock treatment to the fertilized eggs. From the 18th month post-fertilization triploid (TBT) and control diploid (CBT) brown trout groups were investigated up to 32nd month. Survival, specific growth rate, feed conversion ratio, condition factor, relative growth rate, absolute growth rate, gonadosomatic index, hepatosomatic index and carcass yield were determined in both groups. It has been determined that the triploid fish showed greater live weight than diploid fish despite the difference was not significant (P>0.05). In triploid group triploidisation success was obtained as 95% and male/female ratio was found as 44.4-55.6%. The red blood cells were significantly larger in triploids than diploid ones (P<0.05). Regarding histological section of gonads, triploidy resulted in reduced gonadal development in female, while triploid males seem to exhibit normal gonadal development. Our results suggest that since triploid females could grow more than males, the growth performance studies on triploid brown trout should be performed with all-female stocks under fish farming practices especially for the production of large size trout.