With known variation in performance between male and female broilers and the fact that sourcing single-sex birds for use in research is becoming increasingly difficult, it becomes important to determine the effect of rearing method with male and female broilers on between-pen variation and body weight (BW ) uniformity. We evaluated the performance response of broilers reared as single or mixed-sex to standard and reduced crude protein (CP ) diets. The study was designed as a 2 £ 3 factorial arrangement of treatments consisting of 672 Cobb-500 broilers assigned to 48-floor pens with 6 treatments, 8 replicates, and 14 birds per pen. The factors were rearing method (male singlesex, female single-sex, or equally mixed-sex) and dietary CP level (standard or reduced). For the overall period of the trial (d 0−35) there was a significant effect (P < 0.001) of rearing method and CP level on feed intake (FI ) and feed conversion ratio (FCR ). There was also a significant interaction between rearing method and CP level for BWG during d 0 to 35 (P <0.01). There was a significant interaction between CP level and sex on d 34 BW (P <0.01) where the reduced CP diet decreased the BW of both males and females, but to a greater extent the BW of the female birds. Dietary CP level had a significant effect on relative breast and drumstick weights with birds fed the reduced CP diet having significantly lower breast weights (P <0.001) and higher drumstick weights (P <0.01).This study suggests that male and female broilers have different CP requirements, and rearing birds as equally mixed-sex results in the lowest CV% for performance parameters and best BW uniformity compared to single-sex birds. Furthermore, when low CP diets are fed to broilers, they will prioritize the growth of more important body parts such as the legs.