Nonresponse bias was investigated in an outcomes study of adolescent substance abuse treatment. Treatment-related characteristics of respondents (n = 53) were compared with those of non respondents (n = 61). Statistical analysis showed that few differences were seen between respondents and nonrespondents. The results indicate that outcomes data can be collected in this treatment population that are relatively unaffected by nonresponse bias. Missing responses are shown to be very likely missing at random.