<i>Background:</i> While the problem of significant comorbidity in first-episode psychosis (FEP) is well known, little is known about the pattern of onset of disorder prior to and during FEP. The current study examined Axis I psychiatric comorbidity in 62 people being treated for FEP. <i>Method:</i> Morbidity in the years prior to the diagnosis of psychosis was assessed retrospectively, while comorbidities during the 15 months after psychosis diagnosis were investigated prospectively via structured clinical interview. <i>Results:</i> Prevalence of morbidity was high, with 84% of patients having an Axis I psychiatric disorder during at least one phase (i.e. either prior to, during or following the FEP). Sixty-nine percent had one or more psychiatric diagnoses in their lifetime prior to admission for FEP and 47% had one or more comorbid disorder concurrently with FEP. Substance use disorders were most prevalent prior to admission and at 15-month follow-up, while mood disorders were most prevalent during acute psychosis. <i>Conclusions:</i> The study shows the large amount of Axis I comorbidity in young people with FEP. Issues for treatment of comorbidities are discussed.