PURPOSE: To compare polymerase chain reaction (PCR) results to presumptive clinical diagnosis in patients with vitritis. DESIGN: Retrospective review of PCR laboratory records from vitreous samples. METHODS: Fifty consecutive laboratory records of vitreous samples sent for PCR testing were reviewed. Three reviewers with uveitis training ranked the clinical suspicion of a specific diagnosis using a classification system (scale of 1 to 4) and were masked to the PCR results. RESULTS: The degree of clinical suspicion of a particular diagnosis was significantly associated with a positive PCR result (P = .048). Higher clinical suspicion was significantly more associated with a positive PCR result compared with cases with lower clinical suspicion (P = .01). CONCLUSIONS: If the clinical suspicion of a specific diagnosis is low, the PCR for any infectious etiology is unlikely to be positive.