Senna occidentalis is a toxic leguminous plant found in many tropical and subtropical regions of the world and causes poisoning mainly in confined animals. The seeds are the most toxic part of the plant and may be present in animal rations. The main toxic component of the S. occidentalis seed is a dianthrone, an anthraquinone-derived compound that affects mitochondrial function. This study evaluated the effects on egg production of low-level contamination of the S. occidentalis in the laying hens' diet. Forty-eight one-day-old pullets were randomly allocated into two treatment groups: control, birds that received no experimental treatment; and external and internal tegument (ET/IT), birds that received a diet containing 0.2% of ET/IT of S. occidentalis seeds throughout their life cycle (42 weeks). The birds were monitored for clinical signs of poisoning, and the production and quality of eggs were recorded. Necropsies were conducted at the end of the experimental period. None of the layers showed any clinical signs of poisoning, decreases in feed intake or alterations of the body weight gain. A marked reduction in egg production and, consequently, a lower feed efficiency in ET/IT group were measured. Ovaries were the most affected organ in birds from the ET/IT group, and yolk leaking and dysplasia of the inner layer of the vitelline membrane were observed. S. occidentalis was shown to be toxic for laying hens. Considering these results, it is feasible to assume that the constant presence of low concentrations of S. occidentalis seeds in rations represents a threat to the poultry industry.