The Clinical Outcomes in Routine Evaluation Outcome Measure (CORE-OM) is a 34-item self-report measure designed to monitor changes in psychiatric patients. It has been translated into 25 languages, including Finnish. This is the first psychometric exploration of Finnish CORE-OM data. The aim of the study is to examine acceptability, internal consistency and convergent validity of the Finnish CORE-OM scores. Translation of the CORE-OM from English to Finnish was undertaken according to recommended protocols. Psychometric exploration was conducted in two samples: psychiatric patients (N = 201) and non-clinical participants (N = 209). Participation was voluntary and involved completion of all scales. Convergent validity was tested in terms of the mean score differences between clinical and non-clinical samples and correlations against the Beck Depression Inventory (BDI) and the Symptom Checklist (SCL-90). Among the clinical sample, all domains showed good or acceptable internal reliability. In the non-clinical sample, the alphas of domains were good or acceptable, with only the alphas of the Risk domain registering as low. There were no marked gender or age effects. CORE-OM scores correlated strongly with both the BDI and SCL-90, particularly in patients’ data. Some possible effects of Finnish language were found. The Finnish translation of the CORE-OM is psychometrically sound and can be recommended for use in Finnish mental health and clinical settings. However, further investigation in larger and different samples will clarify the generalizability its psychometric properties. Clinical services are encouraged to contribute to the creation of a collaborative Finnish CORE practice research network.