The gonadal histology of 21 prepubertal, intrapubertal, and postpubertal girls who died 1 day to 2 months after cessation of therapy for extragonadal solid tumors was reviewed. In addition to focal or diffuse cortical fibrosis, a reduction in follicle numbers and impaired follicular maturation were observed in cancer patients independent of their pubertal age. These changes appeared to be more severe in malnourished patients and in girls who received multiple agent chemotherapy, with or without irradiation. Both before and after the age of 10 years, most cancer patients had a total number of follicles similar to that of age- and nutrition-matched controls. However, the majority of these girls displayed impaired follicular maturation as demonstrated by reduced numbers of growing and antral follicles compared to controls. Histologic evidence of ovarian damage suggests that the future reproductive performance may be impaired in some female cancer patients treated even before puberty.