Introduction The Patient Health Questionnaire 9-item (PHQ-9) is a 9-item depression screening and diagnostic tool used in primary care and other medical populations to assess presence of depression and its severity. Our aim was to estimate the association between the PHQ-9 questionnaire and fitness for work.

Methods Cross-sectional study of patients who presented at the occupational clinic with a diagnosis of MDD and a PHQ-9 questionnaire was carried out as part of their medical evaluation. From medical records we collected the following characteristics: socio-demographic (age and education data), medical (PHQ-9 score, comorbidities) and occupational characteristics (employment sector, occupation physical demands, scope of employment prior to occupational physician evaluation and the evaluation decision).

Results Out of 165 patients eligible for the study, 125 (75%) agreed to participate and had full details. A negative correlation between depression severity (by PHQ-9 score) and the absolute working ability was found in women (β = −0.36, p = 0.0002) as well as in men (β = −0.4, p = 0.0502). Regarding the relative change in working ability, correlation was found significant for women only (β = −0.33, p = 0.0007) as opposed to men (β = −0.29, p = 0.1664). A multivariate linear regression models adjusted for medical, social, demographic and occupational variables revealed that depression severity (compression group – severe depression, PHQ-9 score ≥ 20) is among the significant predictors of the fitness for work (β = 25.8, p = 0.003 with mild depression, β = 14.7, p = 0.066 for moderate depression) as well as a predictor for the relative change in working ability.

Conclusions We found Correlation exists between absolute and relative fitness for work and depression severity as evaluated by the PHQ-9, accordingly, the higher severity of depression the higher the scope of work disability. The PHQ-9 could be used as a measure in assessing fitness for work.