Objectives:
The goal of this research is to evaluate the psychometric qualities of the Polish version of the SCL-27-plus questionnaire in terms of its five factor structure, internal consistency and theoretical accuracy.

Methods:
A total of 1,350 persons of which 62% were male participated in the study, 651 persons were tested with a paper version, 669 subjects received an electronic version of the questionnaire. 336 (tested with the paper version) were patients with diagnosed psychiatric disorders. Paper version participants also filled out the General Health Questionnaire (GHQ-28).

Results:
Confirmatory factory analysis validated the five factor structure of SCL-27-plus when some errors terms within subscales are allowed to correlate (Depending on the sample: 1.64 ≤ χ²/df ≤ 2.46; 0.05 ≤ RMSEA ≤ 0.06; 0.91 ≤ CFI ≤ 0.95). Cronbach’s Alpha reliability measures for the Global Severity Index was 0.90 to 0.92 and for the particular subscales 0.71 to 0.88. The GSI and symptom subscales for SCL-27-plus correlated with their equivalences in the GHQ-28 moderately to highly (r = 0.38 to 0.68). Strong differences occurred between the “clinical” and “non-clinical” groups in the levels of general and specific symptoms (Cohen’s d from 0.42 to 1.15).

Conclusions:
The Polish version of the SCL-27-plus questionnaire demonstrates good psychometric qualities. It can be used to measure the general intensity of psychopathological impairment as well as the specific subscales.