Hair analyses for drugs of abuse are being increasingly used in both clinical and forensic toxicology, including cases involving children exposed to a drug using environment. A review was conducted of peer-reviewed publications reporting hair concentrations of drugs in children published in the English language. Fifty-two publications were aggregated into three categories: results published on the newborn where hair was sampled at, or shortly after, birth that reflected in utero exposure and/or short-term exposure from the mother s breast milk, and publications in which children were either believed to have been exposed passively from drugs of abuse through their environment or by active exposure from accidental ingestion or deliberate administration by a caregiver. There was limited data for comparison of all three exposure routes. On average, cocaine, codeine, 6-AM and morphine showed higher concentrations in hair from in utero exposure compared to children exposed passively; however, there was considerable overlap in concentrations. Methamphetamine showed no significant difference between passive and in utero exposure, although there was only one study reporting hair concentrations from in utero exposure. There was no difference in concentrations for those cases exposed passively or actively for codeine and methadone. There was insufficient data for other drugs and other comparisons. Comparison data was confounded by the variability in extraction techniques employed as well as a variety of washing techniques, including studies that did not employ any decontamination technique. These data further illustrate the difficulties in interpreting hair concentrations in isolation of relevant contextual data, particularly in children.