Background and Aim: After conducting a comprehensive study on shift work systems in petrochemical companies and recommending appropriate shift schedules, some companies changed shift patterns. After a year, the present study was carried out at a petrochemical company which changed its shift pattern from 4-4-4 to 3-3-3. The objective of the study was evaluation of effectiveness of shift schedule change on shift workers’ health problems.

  Materials and Methods: In this study, samples consisted of 195 shift workers of the present study and 44 shift workers from the previous study. Data were collected by an anonymous questionnaire, in which questions on demographic characteristics, health problems and workers’ opinions about shift pattern change were included. Data were statistically analyzed using SPSS 11.5.

  Results: The results showed that prevalence of gastrointestinal, cardiovascular, and musculoskeletal problems were not statistically different between the two groups (p>0.05), but prevalence of some psychological disorders were lower in the present study subjects as compared to the individuals of the previous study (p<0.01). The results revealed that from the viewpoint of shift workers new shift pattern improved quality and quantity of sleep. The findings showed that 76.8% of the subjects evaluated the new shift schedule to be better than the previous one.