Depression is found in 30-40% of all patients with Parkinson's disease (PD), but its etiology is unclear. Using neuropathology as a signpost for neurotransmitter function, we investigated the prevalence of pathological features found at postmortem and sought to uncover differences between depressed (n=11) and non-depressed (n=9) elderly PD patients. The results indicate a higher prevalence of pathological features in depressed compared to non-depressed PD patients, particularly in catecholamine areas of the brain; the locus coeruleus (neuronal loss: odds ratio=7.2, p=08; gliosis: odds ratio=18.0, p=008); dorsal vagus nerve (gliosis: odds ratio=7.63, p<0.05), and substantia nigra pars compacta (gliosis: odds ratio=2.85, ns). However, neuropathological differences were absent in the dorsal raphe nuclei, amygdala, and cortical regions. Our evidence suggests that depression in PD is related more to catecholaminergic than serotonergic system dysfunction.