The health effects of a Roundup -tolerant genetically modiﬁed maize (from 11% in the diet), cultivatedwith or without Roundup, and Roundup alone (from 0.1ppb in water), were studied 2years in rats. Infemales, all treated groups died 2–3 times more than controls, and more rapidly. This difference was vis-ible in 3 male groups fed GMOs. All results were hormone and sex dependent, and the pathological pro-ﬁles were comparable. Females developed large mammary tumors almost always more often than andbefore controls, the pituitary was the second most disabled organ; the sex hormonal balance was mod-iﬁed by GMO and Roundup treatments. In treated males, liver congestions and necrosis were 2.5–5.5times higher. This pathology was conﬁrmed by optic and transmission electron microscopy. Markedandseverekidneynephropathieswerealsogenerally1.3–2.3greater.Malespresented4timesmorelargepalpable tumors than controls which occurred up to 600days earlier. Biochemistry data conﬁrmed verysigniﬁcant kidney chronic deﬁciencies; for all treatments and both sexes, 76% of the altered parameterswere kidney related. These results can be explained by the non linear endocrine-disrupting effects of Roundup, but also by the overexpression of the transgene in the GMO and its metabolic consequences.