Few studies have investigated maternal aggression toward infants among women with a severe mental illness that emerges in the postpartum period. In this prospective study of 50 Indian women admitted to a psychiatric hospital for severe mental illness occurring in the postpartum period, we examined the prevalence, pattern, and predictors of maternal aggression, infanticidal ideas, and infanticidal behavior. Nearly half (43%) of the mothers reported infanticidal ideas, 36% reported infanticidal behavior, and 34% reported both infanticidal ideas and behavior. Infanticidal ideas and behavior co-occurred frequently (r =.80). Infanticidal ideas were associated with depression in the mother, adverse maternal reaction to separation from the infant, and psychotic ideas toward the infant. Infanticidal behavior was associated with having a female infant, psychotic ideas toward the infant, and adverse maternal reaction to separation from the infant. Logistic regression analyses indicated that presence of depression and of psychotic ideas predicted infanticidal ideas, whereas presence of psychotic ideas toward the infant predicted infanticidal behavior.