OBJECTIVE: Knowledge about course of illness can help clinicians to develop effective interventions and improve treatment outcomes. The goal of this study was to construct positive and negative symptom trajectories based on structured clinical assessments collected over 10years within a cohort of people with first episode psychosis. METHOD: A cohort of 496 people with first episode psychosis (ICD-10, F20-28) originally recruited for the OPUS study (1998-2000) and treated in community psychiatric services were rated on clinical symptoms at 5 different occasions across ten years. Psychopathology was assessed using the Scales for Assessment of Positive and Negative Symptoms. Symptom trajectories were constructed using Latent Class Analysis. RESULTS: Five distinct trajectories were identified for positive symptoms (response - 47%, delayed response - 12%, relapse - 15%, non-response - 13% and episodic response - 13%). Four distinct trajectories were identified for negative symptoms (response - 28%, delayed response - 19%, relapse - 26% and non-response - 27%). Multivariable regression analysis of baseline characteristics identified that longer duration of untreated psychosis (OR 1.27-1.47, p<0.05) and substance abuse (OR 3.47-5.90, p<0.01) were associated with poorer positive symptom trajectories (higher levels of psychotic symptoms) while poor social functioning (OR 1.34-5.55, p<0.05), disorganized symptoms (OR 2.01-2.38, p<0.05) and schizophrenia diagnosis (OR 5.70-8.86, p<0.05) were associated with poorer negative symptom trajectories (higher levels of negative symptoms). A proportion of people displayed significant changes in symptoms several years after diagnosis. CONCLUSIONS: Trajectories of illness for positive and negative symptoms were heterogeneous among people with first episode psychosis. Positive symptoms showed a general pattern of reduction and stabilization over time while negative symptoms typically showed less variation over the ten years. Results have implications for the focus, timing and length of interventions in first episode psychosis.