The presence or absence of 22 schizophrenic symptoms was recorded with the age at onset of illness in 470 patients with non-affective, non-organic psychoses. Positive and negative formal thought disorder, affective symptoms, inappropriate affect, delusions of grandiosity or passivity, primary delusions other than delusional perception, and thought insertion and withdrawal were all more common in early-onset cases (age at onset 44 years or less; n = 336). Persecutory delusions with and without hallucinations, organised delusions, and third-person, running commentary and accusatory or abusive auditory hallucinations were all more common in late-onset cases (age at onset 45 years or more; n = 134). There was no difference between cases of early and late onset in the prevalence of delusions of reference, bizarre delusions, delusional perception, or lack of insight. We conclude that although there are clinical similarities between cases of schizophrenia with early and late onset, there are sufficient differences between them to suggest that they are not phenotypically homogeneous.