The aim of this article is to assess the validity and applicability of medical negligence as a novus actus interveniens, with reference to recent South African criminal case law. Such an assessment necessitates an analysis of the most important rules pertaining to causation in South African criminal law. In the context of medical negligence as a new intervening act, reference is made to the influence of medical errors of judgement and the concept of medical misadventure. The judicial 'grading' of criminal medical negligence as 'gross' or 'overwhelming', with reference to relevant case law, is also explored and criticised. It is submitted that the courts should avoid 'grading' medical negligence by way of policy considerations to establish the absence of a novus actus interveniens. They should rather make a principled assessment of medical negligence, with due consideration to the concepts of medical misadventure and professional errors of judgement. More often than not, a principled assessment will lead to a finding that there was no medical negligence and consequently no novus actus interveniens, even in the face of adverse consequences.