Previous work posits that severity of substance abuse and severity of schizophrenic symptoms should be linked by either or both of two mechanisms: self-regulation of symptoms and drug-induced exacerbation of symptoms. Research on these relationships has yielded mixed results. We examined the interrelationships of schizophrenic symptoms and substance abuse in 172 patients with co-occurring disorders. Relationships were weak or nonexistent, without any consistent pattern. Our findings do not support the view that substances are used to self-regulate symptoms. In addition, our results suggest that substance abuse may lead to higher rates of institutionalization through mechanisms other than by exacerbating symptoms.