Qualitative and quantitative research methods were used to study instances of sudden gains within the case load of a private practice practitioner. Five clients whose progress was marked by such changes were contrasted with the views of five clients whose progress was marked by significant setbacks. Results from the quantitative analyses indicated that clients who experienced sudden gains during therapy tended to retain their therapeutic gains over a 2-year time period. In contrast, individuals who experienced setbacks in therapy generally continued to be distressed at the 2-year reassessment. Clients who experienced sudden gains were more distressed prior to treatment and were more satisfied with their experience looking back. A stronger working alliance was found amongst those who experienced sudden gains, although there was no difference between the groups' ratings regarding the strength of the therapeutic bond. Qualitative results suggested that therapy was helpful in bringing about many changes in clients' lives, but clients who experienced sudden gains generally recalled more positive aspects of therapy, demonstrated greater utilization of therapeutic techniques, endorsed more long-term changes, accepted more responsibility for their treatment outcomes, and were less likely to react negatively to therapeutic techniques. Clients who experienced setbacks in therapy were generally less optimistic about the future, felt that they had regressed since termination, and demonstrated more resistance to therapeutic techniques.