Parental misuse of drugs or alcohol is known to be a common issue for child care social workers, yet there has been surprisingly little British research on the topic. The study reported here attempts to address this gap. All files going for long-term allocation in four London boroughs over on average 1 year were examined (290 files). Parental substance misuse (PSM) emerged as a major feature of social work caseloads. Of the 290 cases, 100 (34%) involved concerns about parental substance misuse. The families involving substance misuse were more vulnerable on a variety of measures: the children were younger, the parents had more individual problems and the families lived in more difficult social situations. PSM cases tended to be 'heavy end' at the point of allocation: they accounted for 62% of all children subject to care proceedings and 40% of those placed on the child protection register. There was a fairly even spread between alcohol and drug misuse, and a number of cases involved both. Substance misuse specialists were rarely involved in working with families, primarily because parents said that they did not think that they had a problem. Suggestions for ways in which policy and practice with PSM might be improved are made in light of these findings.