Enteroviral meningoencephalitis was diagnosed in a patient with an immunodeficiency syndrome acquired after treatment with rituximab for a relapsed primary B-cell lymphoma. A second meningoencephalitic episode was diagnosed 6 months later and was successfully treated with a combination of immunoglobulins and pleconaril. The infection was persistent since the enterovirus genome was detected in five sequential specimens of cerebrospinal fluid collected over 9 months. An echovirus 13 isolate was isolated in the first three samples. The viral sequence encoding the VP1 capsid protein of the three isolates was determined and was compared with that of four control viruses. The virus isolates recovered from the patient shared >99% nucleotide sequence similarity with one another. In a phylogenetic tree, they were directly related to a control virus obtained from a patient hospitalized in 2000 during an outbreak of enterovirus meningitis. The epidemiological origin of a chronic echovirus infection in a patient with immune deficiency suggests that the echovirus had been continuously circulating in the general population after the outbreak that had revealed its emergence.