This study examined the effects of long-term lithium therapy on memory functions in 18 patients suffering from bipolar affective disorder. Patients were retested on the Wechsler Memory Scale, Benton Visual Retention Test, and Zung Self-Rating Depression Scale 6 years after initial testing. Mean memory test scores remained remarkably stable over the 6-year interval with only one of the 10 memory subtests showing a statistically, but not clinically, significant decrease. The sample was split at the median duration of lithium therapy into a long- and shorter term group (with means of 12.9 and 5.2 years, respectively). There were no significant differences between these groups on any of the memory tests when controlled for age and initial memory scores. Negative correlations between several memory test scores and the duration of lithium treatment could in part be explained by the effects of age. Patients' subjective complaints of impaired memory functioning, rated on a visual analogue scale, correlated with the level of depression at the second testing as well as with three memory test scores measuring immediate and short-term visual recall. The results are discussed in view of the demographic and clinical characteristics of the sample and are compared with previous research findings. (J Clin Psychopharmacol 1988;8:207–212)