Aim This study provides a quantitative analysis of registered physicians' task-related cooperation such as care programs, professional networks, quality circles and case conferences. Driving factors of various forms of cooperation are analyzed in a multivariate statistical model to identify starting points for a targeted promotion of medical cooperation. Methods In a random sample of 6,000 practicing physicians in Northern Germany (Bremen, Hamburg, Lower Saxony, Schleswig-Holstein) a number of 504 structured telephone interviews were conducted in August and September of 2014. Results More than 50 % of physicians cooperate in terms of quality circles, case conferences or specialised networks. Older physicians are less likely to cooperate. Urban-rural differences are generally insignificant. The number of physicians per practice is insignificant as to the level of cooperation whereas active involvement in professional associations has a significantly positive effect. Conclusion A high percentage of cooperating physicians shows that the outpatient sector is less fragmented than it often appears to be. The impact of certain practice characteristics on cooperation provides starting points for potential policy measures. Here, our results suggest age-specific measures and further research as to the influence of physicans' involvement in professional associations.