Objectives: This study aimed to assess the proportion of women who underwent postpartum evacuation and were histopathologically confirmed to have retained products of conception (RPOC), compare the reliability of histopathology and ultrasound (US) in determining the presence of RPOC, and assess the maternal complications associated with postpartum evacuation. Methods: A retrospective cross-sectional study was conducted on all women who delivered and had postpartum evacuation at a tertiary teaching hospital in Oman over 11 years from May 2009 to May 2020. The participants were divided into two groups based on their histopathology results. McNemar test was used to compare the sonographic results with the histopathological findings. Results: A total of 151 women were included in this study. The diagnosis of RPOC was confirmed in histopathological reports of 64 (42.4%) women (group 1) but not in 87 (57.6%) women (group 2). There was no significant difference between the two groups in maternal characteristics. Parameters of clinical presentation including fever and abdominal pain were significantly different between the two groups (p = 0.026 and p = 0.028, respectively). Vaginal bleeding was not significantly different between the groups (p = 0.255). Pelvic US detected RPOC in 135 (89.4%) women whereas the histopathology confirmed it in 64 (42.4%) women (p < 0.001). The sensitivity of US compared to histopathology in diagnosing RPOC was 98.4% (95% CI: 91.60–99.96) and the specificity was 17.2% (95% CI: 9.98–26.84). The overall diagnostic accuracy of US in detecting RPOC was 51.7%. Two (1.3%) women had hysterectomy as a result of the evacuation. Histopathology showed smooth muscle in 20 (13.2%) women. Significant bleeding during surgery occurred in 17 (11.3%) cases. Conclusions: Diagnosis of postpartum RPOC is challenging. Our results highlighted the complexity of diagnosing RPOC. Special training is needed for doctors to diagnose RPOC from transvaginal scans. A multicenter study in Oman with a larger sample size is recommended to confirm our findings.