Apathy refers to a reduction in self-initiated behavior, and it is commonly reported by patients infected with human immunodeficiency virus (HIV). It remains unclear whether apathy among HIV patients reflects a direct effect of the virus on subcortical brain circuits or a secondary neuropsychiatric symptom. In the present study we examined the relationship between ratings of apathy and quantitative analysis of the nucleus accumbens (NA), a subcortical brain structure that regulates initiation of behavioral activation. Twelve HIV-positive individuals without dementia were administered the Marin Apathy Scale and underwent neuroimaging. Voxel-based quantification of the nucleus accumbens was completed using a segmentation protocol. Results of our study revealed that increased ratings of apathy were significantly correlated with lower volume of the nucleus accumbens. By contrast, ratings of depression were unrelated to either apathy or nucleus accumbens volume. These findings provide preliminary evidence that apathy reflects direct involvement of the central nervous system in patients with HIV.