In 1970 the medical associations of South Africa and Rhodesia (now, Zimbabwe) were expelled from the Commonwealth Medical Association. The latter had been set up, as the British Medical Commonwealth Medical Conference, in the late 1940s by the British Medical Association (BMA). These expulsions, and the events leading up to them, are the central focus of this article. The BMA’s original intention was to establish an organisation bringing together the medical associations of the constituent parts of the expanding Commonwealth. Among the new body’s preoccupations was the relationship between the medical profession and the state in the associations’ respective countries. It thus has to be seen as primarily a medico-political organisation rather than one concerned with medicine per se. Although, there were also tensions from the outset regarding the membership of the Southern African medical associations. Such stresses notwithstanding, these two organisations remained in the BMA-sponsored body even after South Africa and Rhodesia had left the Commonwealth. This was not, however, a situation which could outlast the growing number of African associations which joined in the wake of decolonisation; and hardening attitudes towards apartheid. The article therefore considers: why the BMA set up this Commonwealth body in the first place and what it hoped to achieve; the history of the problems associated with South African and Rhodesian membership; and how their associations came to be expelled.