Synthetic glucocorticosteroids can induce various severe mental disorders. Persisting cognitive disorder represents a rare complication of corticoid therapy involving memory, concentration, attention, or occupational performance. We observed the effects of a 20-day self-induced high-dose corticosteroid treatment on the cognitive functions in a 54-year-old patient. Having excluded dementia due to other organic causes, we examined the patient neuropsychologically immediately at the end of the steroid therapy and at follow-up (1, 2, 4, and 6 months). The initial tests showed seriously impaired functioning of concentration, attention, learning, and memory as well as of common ability to solve problems. The follow-up tests up to 6 months revealed an improvement of concentration and attention, but there were still serious deficits of the declarative memory with a high confabulating tendency. Our results confirm those of human experimental studies that exogenous steroids can cause serious persisting specific cognitive disorders especially of the declarative, hippocampus-dependent memory.