Background: The purpose was to investigate the association between the working hour characteristics of irregular working hours and the first incident occupational accident in the retail sector. Methods: Employer-owned register data of daily working hours and the first incident occupational accidents in 2021-2023 were used. The final sample of 470 employees was analyzed using a casecrossover design to obtain odds ratios (ORs) with 95% confidence intervals (95% CI) for the seven-day periods of working hours preceding the accidents. Results: The weekly working hours (OR: 1.02-1.03, 95% CI: 1.00-1.08), shift length (OR: 10.12-12.47, 95% CI: 4.73- 32.9), and evening shifts (OR: 1.02, 95% CI: 1.01-1.04) were associated with an increased likelihood of occupational accidents among both part- and full-time employees. Early morning (OR:1.03, 95% CI: 1.01-1.04) and morning (OR: 1.02, 95% CI: 1.01-1.03) shifts, and the percentage of short (<4 hour) shifts (OR: 1.06, 95% CI: 1.01-1.12) increased the likelihood of occupational accidents among parttime employees, and the number of consecutive work shifts (OR: 1.55, 95% CI: 1.04-2.30) among fulltime employees. Conclusion Working evenings and the length of work shifts, or weekly working hours, even for 7 days, were associated with an increased likelihood of occupational accidents among both part-time and fulltime employees. Since early morning and morning shifts showed an increased risk among part-time employees, special attention should be paid to them. Thus, shift scheduling in the retail sector merits attention to regularity and avoidance of long or early shifts, supplemented with safety instructions to ensure the health and safety of employees.