OBJECTIVES Neurologic infections caused by cytomegalovirus are common in patients with acquired immunodeficiency syndrome (AIDS). The prognosis is particularly severe when the infection is localized in the conus medullaris and/or the cauda equina. METHODS Among the 861 patients with AIDS treated in our unit from 1991 to 1993, 7 cases involving cytomegalovirus infection of the conus medullaris and/or the cauda equina were studied retrospectively. RESULTS OF THE CASE REPORTS: Clinical manifestations were nearly always the same: low back pain, motor deficiency in the lower limbs progressing to flaccid paraplegia and sphincter failure. The cerebrospinal fluid contained a high cell count with unaltered polynuclears and increased protein levels. In 6/7 patients virus cultures and search for the viral genome in the cerebrospinal fluid were positive. The clinical course was favourable in 6 patients after 3 weeks treatment with ganciclovir and/or foscarnet. Virology tests became negative in three-fourths of the patients. Nevertheless, relapse occurred after 4.2 weeks despite long-term therapy. CONCLUSION The severe clinical course of this disease and the gravity of constantly fatal relapse requires highly adapted treatment and overall health care.