Narcolepsy is a chronic sleep disorder that affects human beings and animals. Up to 17 breeds of dogs are affected sporadically, and familial forms occur in dobermanns, labrador retrievers and dachshunds. These dogs display characteristics strikingly similar to those of human narcolepsy, including cataplexy (a sudden loss of muscle tone in response to emotional stimulation) and a shorter sleep latency. It has recently been shown that the aetiology of both the familial form (receptor null mutation) and the sporadic form (loss of ligand production) of canine narcolepsy is associated with a deficit in hypocretin/orexin neurotransmission. Hypocretin deficiency can be detected by the measurement of hypocretin-1 in cerebrospinal fluid, and this could be used to diagnose hypocretin ligand deficient cases in clinical practice. Narcolepsy is neither progressive nor life-threatening, but the clinical signs persist throughout life, and lifelong treatment and care are required. This article reviews the recent progress in narcolepsy research in dogs, and describes the diagnosis and treatment of the disease.