We examined comorbid psychiatric and neurodevelopmental disorders in fifty adult males (mean age 30 years) with Asperger syndrome (AS) diagnosed in childhood and followed up prospectively for almost two decades (13-26 years). Only three of the 50 men had "never" met criteria for an additional psychiatric/neurodevelopmental diagnosis and more than half had ongoing comorbidity (most commonly either ADHD or depression or both). Any psychiatric comorbidity increased the risk of poorer outcome. The minority of the AS group who no longer met criteria for a full diagnosis of an autism spectrum disorder were usually free of current psychiatric comorbidity. The high rate of psychiatric/neurodevelopmental comorbidities underscores the need for a full psychiatric/neurodevelopmental assessment at follow-up of males with AS.