ObjectiveWhether care group participation by general practitioners improves delivery of diabetes care is unknown. Using ‘monitoring of biomedical and lifestyle target indicators as recommended by professional guidelines’ as an operationalisation for quality of care, we explored whether (1) in new practices monitoring as recommended improved a year after initial care group participation (aim 1); (2) new practices and experienced practices differed regarding monitoring (aim 2).DesignObservational, real-life cohort study.SettingPrimary care registry data from Eerstelijns Zorggroep Haaglanden (ELZHA) care group.ParticipantsAim 1:From six new practices (n=538 people with diabetes) that joined care group ELZHA in January 2014, two practices (n=211 people) were excluded because of missing baseline data; four practices (n=182 people) were included.Aim 2:From all six new practices (n=538 people), 295 individuals were included. From 145 experienced practices (n=21 465 people), 13 744 individuals were included.ExposureCare group participation includes support by staff nurses on protocolised diabetes care implementation and availability of a system providing individual monitoring information. ‘Monitoring as recommended’ represented minimally one annual registration of each biomedical (HbA1c, systolic blood pressure, low-density lipoprotein) and lifestyle-related target indicator (body mass index, smoking behaviour, physical exercise).Primary outcome measuresAim 1:In new practices, odds of people being monitored as recommended in 2014 were compared with baseline (2013).Aim 2:Odds of monitoring as recommended in new and experienced practices in 2014 were compared.ResultsAim 1:After 1-year care group participation, odds of being monitored as recommended increased threefold (OR 3.00, 95% CI 1.84 to 4.88, p<0.001).Aim 2:Compared with new practices, no significant differences in the odds of monitoring as recommended were found in experienced practices (OR 1.21, 95% CI 0.18 to 8.37, p=0.844).ConclusionsWe observed a sharp increase concerning biomedical and lifestyle monitoring as recommended after 1-year care group participation, and subsequently no significant difference between new and experienced practices—indicating that providing diabetes care within a collective approach rapidly improves registration of care.