For patients first presenting with a non-affective psychotic disorder, the duration of untreated psychosis (DUP; the time between the onset of positive psychotic symptoms and the initiation of appropriate treatment) varies widely, from a few weeks to several years. A number of studies report that a longer DUP is associated with poorer clinical outcomes. We studied DUP and its association with clinical outcomes in a group of patients with schizophrenia and related psychotic disorders treated in the naturalistic clinical setting of an early psychosis program. DUP was determined for 19 patients with a non-affective psychotic disorder (schizophrenia, schizoaffective disorder or schizophreniform disorder) and no previous treatment for psychosis, by use of the IRAOS, a retrospective structured interview carried out with patients and their families. Positive and Negative Syndrome Scale (PANSS) and Global Assessment of Function (GAF) ratings were available at baseline and 6month follow-up. For analysis, patients were categorized into a short DUP (n=9) or long DUP (n=10) group. The median DUP (57weeks) was used as the dividing point. At baseline, the two groups did not differ significantly on positive symptoms or total PANSS ratings. However, negative symptoms were more severe in the long DUP group at baseline (P=0.029), and the long DUP group had a significantly higher mean rating for the passive/apathetic social withdrawal item of the PANSS (P=0.024). At 6month follow-up, the long DUP group had significantly higher ratings for positive symptoms (P=0.028) and had lower GAF scores (P=0.044). Significantly more (P=0.033) long DUP patients had enduring positive psychotic symptoms. The results confirm both the wide range of DUP among patients first presenting with schizophrenia and related psychotic disorders and the association of long DUP, defined as greater than approximately 1year, with a poorer clinical outcome. This study highlights the importance of collecting data regarding DUP and supports the view that patients with a long DUP are likely to be less responsive to treatment in general and will require greater resources and more intensive interventions.