The likelihood of being reported to an addict registry before and after admission to a methadone treatment program in Hong Kong was determined for all 1,908 patients who enrolled during May and June 1978. In the 6 months before enrollment, two out of every five patients had contact with at least one reporting source, and 10% of all patients had contact with a criminal justice system agency. Cohorts grouped according to retention in treatment did not differ with respect to preadmission reporting experience. Following enrollment, however, these cohorts demonstrated a very strong association between continued treatment and a decreased likelihood of contact with a reporting source: 13% of continuously active patients were reported during the 6 months after enrollment, compared to 68% of those who dropped out of treatment within 2 months; the corresponding reporting history from criminal justice system agencies was 6 and 23%, respectively. The association between retention and decreased contact with reporting agencies was observed for each age group studied.Following discharge, the cumulative likelihood of being reported rapidly approached that of patients leaving treatment earlier.