The present study examines the extent of turnover in mental health provider networks within public sector managed mental health care over a 1-year period and its association to provider and practice characteristics. Telephone interviews were conducted with a sample of mental health services providers listed the previous year in the networks of the 3 public sector managed mental health care organizations operating in Puerto Rico. Thirty-one percent of respondents had dropped out of networks. The drop-out rate was significantly associated (P≤.05) with increasing number of years in practice and decreasing years under contract. A nonsignificant trend was observed, suggesting that providers with subspecialty training are less likely to drop out. The results may be signaling an emerging problem in public sector managed mental health care. Stability of provider networks should be monitored by state agencies contracting out mental health care.