Ramelteon is a nonscheduled insomnia medication that lacks the abuse potential and residual effects common for other sedative-hypnotics. Distinct in its mechanism, the drug is a melatonin agonist with a high affinity for the membrane receptors MT1 and MT2. Although it therapeutically targets the suprachiasmatic nucleus of the hypothalamus, many organ systems have melatonin receptors and thus may be influenced by ramelteon. A growing body of research on melatonin indicates that it modulates the immune system. Indeed, immune cells have been shown to synthesize and to respond to this compound through receptors including MT1 and MT2. Melatonin's effects are generally immunostimulatory, and there is evidence to suggest that the chemical may potentiate autoimmunty. Here, we describe a case of autoimmune hepatitis that developed in a 50-year-old man after starting ramelteon for insomnia. The temporal association between ramelteon initiation and disease development, as well as the immunomodulatory properties of melatonergic compounds, suggest a role for ramelteon in the etiology of his illness.