Background: Nearly one third of patients suffering from schizophrenia do not fully respond to antipsychotic medication. Safe, effective, and cost- efficient methods to reduce symptoms are clearly needed; therefore, lithium as an adjunct to fluphenazine decanoate was tested in a placebo-controlled trial in outpatients who were part of the Treatment Strategies of Schizophrenia (TSS) study. Method: Forty-one patients with DSM-III schizophrenia or schizoaffective disorder were assigned to either adjunctive lithium or placebo after at least 6 months of fluphenazine decanoate treatment to stabilize symptoms had failed. The trial was designed for 8 weeks of treatment, and patients assigned to placebo could afterward be administered lithium in an 8-week, open-label study. Results: Assessment of the intent-to-treat analysis revealed no significant differences in demographic variables between the lithium and placebo groups. Although both groups showed significant (p = .00135) improvement as measured by total scores on the Brief Psychiatric Rating Scale (BPRS), there were no significant differences in response between the lithium and placebo groups. Patients originally treated with placebo added to neuroleptic did not have significantly greater improvement when receiving open-label adjunctive lithium. Conclusion: Although success with lithium augmentation therapy for persistent psychosis has been reported in the past, this study of well- characterized patients showed no benefit for this common strategy, thus indicating that care be used in utilizing lithium augmentation.