OBJECTIVE. The objective of this study was threefold: to determine if the frequency of deep white matter changes and cerebral atrophy seen on MR images is significantly different between patients with and without AIDS dementia complex, to determine if certain patterns of white matter changes are more closely associated with AIDS dementia complex, and to determine if focal lesions within the white matter of the splenium are more common in AIDS dementia complex. MATERIALS AND METHODS. Forty-five patients with AIDS were clinically examined for AIDS dementia complex. MR images from these patients were retrospectively reviewed without knowledge of the clinical results. The presence or absence of white matter abnormalities and cerebral atrophy was evaluated by using graded scales and correlated with the presence or absence of AIDS dementia complex. RESULTS. Ten patients met the criteria for AIDS dementia complex. Eight of 25 patients in whom MR images showed abnormal signal intensity in deep white matter had dementia compared with two of 20 in whom MR showed no changes in deep white matter. The presence of these deep white matter abnormalities was not significantly different between groups with and without dementia (p = .08), although higher grades of deep white matter abnormality were more likely to be associated with AIDS dementia complex. Nine of 19 patients in whom MR images showed atrophy had dementia compared with one of 26 in whom MR showed no atrophy. Atrophy was significantly associated with AIDS dementia complex (p = .001). Eight of 15 patients in whom MR images showed abnormal signal intensity within the white matter of the splenium had dementia compared with two of 30 in whom MR showed normal signal intensity in this area. The degree of abnormality in the splenium was weakly associated with AIDS dementia complex (Kendall's tau = .471, p = .001). CONCLUSION. MR findings of cerebral atrophy and abnormal signal intensity in the splenium are associated with AIDS dementia complex. The presence of generalized deep white matter abnormalities does not differ significantly between patients with and without dementia, although more severe grades of white matter abnormality are more likely to be seen in patients with AIDS dementia complex.