Aims: The study objective was to develop a clinical risk score to assist occupational medicine physicians in diagnosing hospital workers’ occupational lower back pain (LBP). Settings and Design: A cross-sectional data collection design was conducted at Saraburi Hospital, Thailand. Methods and Materials: The sample consisted of 220 hospital workers who cared for patients and had LBP. They were assessed for the frequency of targeted activities (CPR, lifting, transferring patients) and other activities from work as well as ergonomic assessments, and diagnosed with LBP by three occupational medicine physicians. Statistical Analysis Used: Predicted factors of multivariable logistic regression were analysed to find clinical risk scores to help the diagnosis. Results: The physicians agreed on the diagnosis, based on ergonomic risk factors and their experiences that 86 persons have occupational LBP. A diagnostic assistant tool consists of six predictors: the duration of LBP, having LBP within the last 7 days, bending, twisting, lateral bending, and reaching. The scores predicted occupational LBP correctly with an AuROC of 90.0% (95% CI; 84.8–93.5%). The positive likelihood ratio for occupational LBP was 0 in the low risk category (<6 points) and 16.8 (95% CI; 8.0–35.6) in the high risk (>8 points). Conclusions: A diagnostic assistant tool is used to assist occupational medicine physicians in diagnosing hospital workers' occupational LBP.