The author proposes a pathogenesis for the bizarre, repetitive behaviors frequently seen in deteriorated schizophrenics, i.e., polydipsia, hoarding, pacing, etc. It is argued that such behaviors may have a neurobiology similar to schedule-induced behaviors or incentive-conditioned behaviors described in animal models, which involve the hippocampus, nucleus accumbens, and the neurotransmitter dopamine. Such behaviors are augmented by hippocampal lesions, stress, increased drive state, or dopaminergic agents, and reduced by 6-OH dopamine lesions to nucleus accumbens or antipsychotic agents. These repetitive behaviors may reflect the failure of hippocampus to modulate the impact of mesolimbic dopaminergic activity on the nucleus accumbens and thus on motor behavior. Such a hypothesis is consistent with a growing body of neuropathological and brain imaging results demonstrating hippocampal lesions in chronic schizophrenics.