It has been suggested that the use of covert video surveillance in suspected cases of Munchausen syndrome by proxy should be curtailed as it represents a breach of trust between health care workers, parents and children. We present a case of asphyxia induced by a mother, which was discovered by videotaping without consent. Two previous sudden infant deaths in the family over the preceding two years, with unexplained apnoeic episodes in the third child, were considered sufficiently suspicious to justify covert surveillance. Incontrovertible evidence of parentally induced asphyxia was obtained within 24 hours of full-time covert surveillance. Despite initial denial, the mother eventually pleaded guilty to manslaughter of the first infant and to causing grievous bodily harm to the third infant. We believe that alternative techniques, such as parent-child separation, or of videotaping only after informed consent has been obtained, could have compromised the investigation and produced unacceptable delays which would have placed the surviving infant at risk of serious morbidity or of death.