BACKGROUND: Comorbidity between Attention Deficit Hyperactivity Disorder (ADHD) and mood disorders is common. Alterations of the cerebellum and frontal regions have been reported in neuro-imaging studies of ADHD and major depression. METHODS: Thirty chronically depressed adult females of whom 16 had scores below, and 14 scores above, cut-offs on the 25-items Wender Utah Retrospective Scale (WURS-25) and the Wender-Reimherr Adult Attention Deficit Disorder Scale (WRAADDS) were divided into subgroups designated "Depression" and "Depression + ADHD", respectively. Twenty-one of the patients had some audiological symptom, tinnitus and/or hearing impairment. The patients were investigated with other rating scales and 99mTc-HMPAO SPECT. Controls for 99mTc-HMPAO SPECT were 16 healthy females. SPECT was analyzed by both statistical parametric mapping (SPM2) and the computerized brain atlas (CBA). Discriminant analysis was performed on the volumes of interest generated by the CBA, and on the scores from rating scales with the highest group differences. RESULTS: The mean score of a depression rating scale (MADRS-S) was significantly lower in the "Depression" subgroup compared to in the "Depression + ADHD" subgroup. There was significantly decreased tracer uptake within the bilateral cerebellum at both SPM and CBA in the "Depression + ADHD" subgroup compared to in the controls. No decrease of cerebellar tracer uptake was observed in "Depression". Significantly increased tracer uptake was found at SPM within some bilateral frontal regions (Brodmann areas 8, 9, 10, 32) in the "Depression + ADHD" subgroup compared to in "Depression". An accuracy of 100% was obtained for the discrimination between the patient groups when thalamic uptake was used in the analysis along with scores from Socialization and Impulsivity scales. CONCLUSION: The findings confirm the previous observation of a cerebellar involvement in ADHD. Higher bilateral frontal 99mTc-HMPAO uptake in "Depression + ADHD" compared to in "Depression" indicate a difference between these subgroups. 99mTc-HMPAO uptake mechanisms are discussed.