Background: Hospitals are one of the most important units in providing healthcare services. The assessment of the quality of provided services is essential in these settings. Patient satisfaction is one of the key indicators of service quality in healthcare organizations. Objectives: This study aimed at investigating the gap between the perceptions and expectations of service recipients in Shohada-e-Tajrish Hospital (Tehran, Iran), using the SERVQUAL model in 2020. Methods: This cross-sectional study was conducted on patients with cancer, who were upon discharge from Shohada-e-Tajrish Hospital. Patients (> 18 years) with a cancer diagnosis, who were being discharged from the oncology ward of the hospital, were included in this study. The sample size was estimated at 118. The required information was collected, using the modified SERVQUAL questionnaire. Statistical analyses were performed in SPSS version 20, using a paired t test and one-sample t-test. Results: The results showed that the quality of the provided services from the patients’ perspective was significantly lower than their expectations. The mean gap between the expectations and perceptions of patients was significantly above zero (P < 0.001). The most influential factor in improving patient satisfaction with the quality of services was assurance, followed by reliability, while the least effective factor was empathy. The correlation coefficient between the general status of provided services from the patients’ point of view and loyalty was 0.740 (P < 0.001). Conclusions: The findings of the present study indicated that patient expectations were higher than their satisfaction. Therefore, hospital authorities should take major steps to improve the quality of services, especially reliability and responsiveness, through proper planning, prioritization of services, and review of processes contributing to patient expectations. The existing gaps can also be addressed by considering the perspectives of patients as the clients of healthcare organizations.