Cancer is a rare but devastating diagnosis to make during pregnancy. It poses a significant challenge to obstetricians, oncologists, paediatricians and radiologists alike, who must work in close communication with the affected family, and with each other, to provide individualized care. The evidence available to guide management decisions is often retrospective and prone to bias and these uncertainties only add to the psychological distress. This article sets out some of the general principles involved and gives a number of examples to illustrate these points.