Objective: To compare the image quality (IQ), radiation dose and diagnostic reliability of standard-dose and low-dose lumbar spine (L-spine) multi-detector CT (SDCT and LDCT, respectively) with iterative reconstruction (IR) in trauma patients. Methods: We retrospectively analysed the data of 263 consecutive patients (male:female, 133:130; mean age, 44.3 years) who underwent SDCT (200-300 mAs; 120 kVp) with IR (n = 126) or LDCT (80-150 mAs; 120 kVp) with IR (n = 137) for suspected L-spine fractures between November 2015 and September 2016. Patients were categorized according to their body mass index, as follows: Group 1, ~22.9 kg m-2; Group 2, 23-24.9 kg m-2 or Group 3, c 25 kg m-2. We compared the quantitative IQ (signal-to-noise ratio), qualitative IQ (subjective image noise and diagnostic acceptability [4-point rating scale; score 1-4], image sharpness [5-point rating scale; score 1-5]) and diagnostic accuracy between the two scan types. Interobserver agreement was also calculated. Results: Overall, SDCT exhibited slightly better diagnostic performance than did LDCT (sensitivity, 96.7-100% vs 94-98.5%; specificity, 95.6-97.0% vs both 95.7%; accuracy, 96.0-98.4% vs 94.9-97.1%). However, none of these parameters was significantly different between SDCT and LDCT, either in the whole cohort (p ≥ 0.50) or among the three body mass index groups (p ≥ 0.49). All interobserver agreements were excellent or good (range, 0.776-0.985). Conclusions: The diagnostic performance of LDCT with IR for L-spine fractures was comparable to that of SDCT with IR, with a 47-69% reduction in the radiation dose. Advances in knowledge: LDCT scan can be used as a diagnostic imaging tool for evaluating trauma patients with suspected L-spine fractures.