Excessive grooming behaviors, cleansing rituals, and self-mutilation are important features of a range of neuropsychiatric diseases including obsessive compulsive (OC)-spectrum disorders. In this issue of Neuron, Greer and Capecchi (2002) report that Hoxb8 mutant mice exhibit this behavioral phenotype. These Hoxb8 mutants will be valuable in exploring the genetics and pathophysiology of OC-spectrum disorders as well as strategies for their treatment.