Cognitive impairment in long-term high-dose diazepam abusers (dose > 30 mg diazepam/day; duration of abuse > 12 months) was examined by administering four memory-related tests and comparing the outcomes with those of matched controls. Deficits were found in spatial and visual learning, spatial and visual short-term memory (STM) as well as for spatial and visual long-term memory (LTM). As for verbal aspects of memory, solely the acquisition of novel verbal material (verbal learning) was impaired, Furthermore, deficits in a concentration task were observed. In chronic abuse the established memory deficits are similar to cognitive impairment after single doses. Relaxing or anxiety-reducing effects of diazepam were no longer present. The results of this experimental study demonstrate the risks of diazepam use beyond therapeutic range.