Objective This study aimed to identify and point out the number and types of medication discrepancies among cancer patients admitted to Jordan University Hospital. Method This is a cross-sectional observational study that was conducted on cancer patients in the internal medicine department at Jordan University Hospital, Amman, Jordan. During a period of six months, a convenience sample of cancer patients was recruited, and their medical records were reviewed to collect information regarding their demographics, clinical, and medication information. Also, patients’ Best Possible Medication History (BPMH) was collected using different methods, and a comparison between patients’ BPMH and their current medications was conducted where discrepancies were recognized. Results Seventy-eight medical records were reviewed, with a total of 166 discrepancies identified. Of these, 110 discrepancies (66.3%) were unintentional. Exactly 67.9% of the study participants ( n = 53) were found to have at least one unintentional discrepancy, with the most common type being omissions ( n = 71, 65.1%,) and the second most common type being additions ( n = 16, 14.7%). Most of the discrepancies ranged between low to moderate in severity. Fifty-six (33.7%) intentional undocumented discrepancies (documentation errors) were also identified. Conclusion This study revealed a high rate of medication discrepancies among hospitalized cancer patients, most commonly unintentional omissions. Nevertheless, undocumented intentional discrepancies can equally harm this critically ill population. So, do we need medication reconciliation in cancer patients? Yes. Cancer patients are critically ill, and therefore more effort should be paid towards implementing medication reconciliation services in their treatment plan.