Seizures were induced in female Wistar albino rats at either 35 or 55 days of age with a single systemic injection of lithium (3 mEq/kg) and pilocarpine (30 mg/kg); the rats were then treated with the atypical neuroleptic acepromazine (25 mg/kg). These rats manifested progressive weight gain for the rest of their lives. The effect was conspicuous by casual observation 6 weeks after treatment and occurred primarily in those rats that later developed spontaneous seizures. After 1 year, the rats were obese (>1000 g). Such weight gains, associated with almost three times the serum triglyceride levels, were not observed in male rats and have not been observed in hundreds of female rats that received this treatment as adults. Single postseizure injections of ketamine rather than acepromazine did not produce this obesity; the weights of these rats were similar to those of normal littermates. These results indicate that a single injection of a neuroleptic during limbic seizures before puberty can produce neuronal alterations that contribute to a lifetime of obesity.