Clinically significant pain (CSP) is one of the most common complaints among cancer patients during repeated hospitalizations, and the prevalence ranges from 24% to 86%. This study aimed to characterize the trends in CSP among cancer patients and examine the differences in the prevalence of CSP across repeated hospitalizations. A hospital-based, retrospective cohort study was conducted at an academic hospital. Patient-reported pain intensity was assessed and recorded in a nursing information system. We examined the differences in the prevalence of worst pain intensity (WPI) and last evaluated pain intensity (LPI) of ≥ 4 or ≥ 7 points among cancer inpatients from the 1st to the 18th hospitalization. Linear mixed models were used to determine the significant difference in the WPI and LPI (≥ 4 or ≥ 7 points) at each hospitalization. We examined 88,133 pain scores from the 1st to the 18th hospitalization among cancer patients. The prevalence of the 4 CSP types showed a trend toward a reduction from the 1st to the 18th hospitalization. There was a robust reduction in the CSP prevalence from the 1st to the 5th hospitalization, except in the case of LPI ≥ 7 points. The prevalence of a WPI ≥ 4 points was significantly higher (0.240-fold increase) during the 1st hospitalization than during the 5th hospitalization. For the 2nd, 3rd, and 4th hospitalizations, there was a significantly higher prevalence of a WPI ≥ 4 points compared with the 5th hospitalization. We also observed significant reductions in the prevalence of a WPI ≥ 7 points during the 1st to the 4th hospitalizations, an LPI ≥ 4 points during the 1st to the 3rd hospitalizations, and an LPI ≥ 7 points during the 1st to the 2nd hospitalization. Although the prevalence of the 4 CSP types decreased gradually, it is impossible to state the causative factors on the basis of this observational and descriptive study. The next step will examine the factors that determine the CSP prevalence among cancer patients. However, based on these positive findings, we can provide feedback to nurses, physicians, and pharmacists to empower them to be more committed to pain management.