Treatment in Psychiatry begins with a hypothetical case illustrating a problem in current clinical practice. The authors review current data on prevalence, diagnosis, pathophysiology, and treatment. The article concludes with the authors' treatment recommendations for cases like the one presented.Mrs. A, a 34-year-old married mother who lived with her husband and their 5-year-old daughter, strangled her infant son to death 3 weeks after birth. She had a planned, healthy pregnancy with some depression at 28 weeks' gestation. She had a normal spontaneous vaginal delivery, giving birth to a healthy boy, "B." She began breastfeeding immediately. From postpartum days 2 through 11, her depression worsened. She was unable to sleep but could not get out of bed or attend to her hygiene. She was suspicious that her husband would harm B. On postpartum day 2, she began having obsessional, ego-dystonic images of throwing B out the window. She believed, despite the pediatrician's reassurances, that she was harming B with her breast milk and that he was losing weight. She was unable to give him a bath, believing that he had "gas" or "something bad" inside and could not be moved.On day 12, while alone in the car with B, she thought of killing herself and the baby, although "at the time I don't think I had any idea why." On day 13, she attempted suicide by overdose. She slept through the night and did not report the suicide attempt to anyone. She abruptly weaned B and then became disorganized and confused, unsure of what formula and size and types of bottles and nipples to use. She was agitated, calling friends day and night for opinions. On day 15 she attempted to smother B with a towel. "I don't believe it was a thought," she said. "It was 'autopilot.'" Her husband came upstairs, and Mrs. A believes that his presence shook her out of the "state" she was in. "I did not have the compulsion to hurt him any more after that evening … I just thought something was wrong, and I wasn't thinking straight." Her husband knew that she was not herself, but he did not understand that she was depressed and psychotic. Mrs. A did not receive treatment for her illness.On postpartum day 20, Mrs. A awoke at 6: 30 a.m. to feed B when he cried. Her husband and daughter kissed her goodbye, and Mr. A walked their daughter to school before going to work. She soon felt as if she was "taken over." She describes a dazed, trance-like state with confusion: "Something internal like a force … it was not a voice … but I did not have control. It was an instant. I don't recall thinking anything … I had no feelings. It was happening but I wasn't there.… At the time, nothing came into my head saying, 'No, do not do this.' … My inside was gone and it was something else." She briefly placed a towel over B's nose and mouth, but stopped. The "force" then became intense. She placed a washcloth in B's mouth and then strangled him with a telephone cord. She felt she was not connected to her own hands. When B was dead, she washed him with a cloth, removed the remnants of h...