Objective To test the effectiveness of educational interventions in improving detection rates and management of dementia in primary care. Design Unblinded, cluster randomised, before and after controlled study. Setting General practices in the United Kingdom (central Scotland and London) between 1999 and 2002. Interventions Three educational interventions: an electronic tutorial carried on a CD Rom; decision support software built into the electronic medical record; and practice based workshops. Participants 36 practices participated in the study. Eight practices were randomly assigned to the electronic tutorial; eight to decision support software; 10 to practice based workshops; and 10 to control. Electronic and manual searches yielded 450 valid and usable medical records. Main outcome measures Rates of detection of dementia and the extent to which medical records showed evidence of improved concordance with guidelines regarding diagnosis and management. Results Decision support software (P = 0.01) and practice based workshops (P = 0.01) both significantly improved rates of detection compared with control. There were no significant differences by intervention in the measures of concordance with guidelines. Conclusions Decision support systems and practice based workshops are effective educational approaches in improving detection rates in dementia.