The incidence, factor structure and scale item differences in anxiety-depression comorbidity were investigated in a sample of Australian university students defined according to the presence of anxiety and/or depression. The incidence of anxiety-depression comorbidity was over 32%, about four times that for anxiety or depression alone. Participants with comorbidity had significantly higher Self-rating Anxiety Scale (SAS) and Self-rating Depression Scale (SDS) total and factor scores than those with anxiety or depression alone. The major differences between the comorbid and unitary disordered subgroups were for self-disintegration and autonomic arousal. Comorbidity of anxiety and depression is a more serious disorder than either anxiety or depression alone, and appears to exist in large proportions among university students. Assessment and treatment plans might benefit from inclusion of this comorbidity.