Implementation of routine outcome monitoring (ROM) in mental health care is progressing slowly. Knowledge about factors influencing ROM implementation, including health providers' attitudes towards ROM, is necessary. Based on a survey of 662 psychologists and nurses, this article describes (1) the development of a short instrument measuring provider attitudes towards ROM, derived from the Evidence-based Practice Attitude Scale (EBPAS), and (2) how attitudinal domains relate to clinicians' current use of standardized instruments for treatment evaluation. The EBPAS-ROM showed concurrent validity in predicting aspects important for the implementation of ROM, including perceived limitations and the value of organizational support.