The effects of light intensity during rearing and beak trimming and dietary fiber sources on the incidence of cannibalism were investigated with 2,880 ISA Brown hens. During the rearing period, chicks were housed under two levels of light: dim light (i. e., 5 lx) and bright light (i. e., 60 to 80 lx) and two beak conditions: with or without trimming. At 15 wk of age, all birds were transferred to laying cages with five birds per cage. At 17 wk of age, four diets containing different concentrations of dietary fiber were offered: a commercial (wheat) diet, high insoluble fiber (millrun) diet, high soluble fiber (barley) diet, and high soluble fiber diet plus enzyme. Beak trimming had a profound effect (P < 0.001) on cannibalism with mortality occurring predominantly in untrimmed birds. Total mortality for the trimmed birds was 0.14 and 0.77% for the prelay (17 to 20 wk) and early lay periods (21 to 24 wk), whereas mortality was 13.4 and 37.7%, respectively, for the untrimmed birds. The beak-trimmed birds had lower feed intake than the nontrimmed birds (P < 0.05). Diet significantly affected cannibalism (P < 0.01). The highest mortality occurred in birds fed the commercial diet (13 and 29% for the prelay and early lay period, respectively). Diet also affected feed intake (P < 0.05), being lower (P < 0.05) on the commercial diet than on the higher fiber diets. Egg production per bird did not differ significantly between diets. Light intensity during rearing did not influence the incidence of cannibalism.