Di(n-butyl) phthalate (DBP) is commonly used in personal care products and as a plasticizer to soften consumer plastic products. Male rats exposed to DBP in utero have malformations of the male reproductive tract and testicular atrophy characterized by degeneration of seminiferous epithelium and decreased sperm production. In the fetal testis, in utero exposure to DBP reportedly resulted in reduced testosterone levels, Leydig cell aggregates, and multinucleated gonocytes (MNG). We investigated whether exposure in utero to DBP affects rat fetal Sertoli cells and compromises interactions between Sertoli and germ cells in the developing testis. Histological examination showed that MNG occurred at low frequency in the normal fetal rat testis. Exposure in utero at the dose level of DBP above estimated environmental or occupational human exposure levels significantly increased the number of these abnormal germ cells. Postnatally, MNG exhibited aberrant mitoses and were detected at the basal lamina. MNG were not apoptotic in the fetal and postnatal rat testes, as indicated by TUNEL. Sertoli cells in DBP-exposed fetal testis had retracted apical processes, altered organization of the vimentin cytoskeleton, and abnormal cell-cell contacts with gonocytes. The effect of DBP on Sertoli cell morphology at the level of light microscopy was reversed after birth and cessation of exposure. Our data indicate that fetal Sertoli cells are targeted by exposure in utero to DBP and suggest that abnormal interactions between Sertoli and germ cells during fetal life play a role in the development of MNG.