Background: Increasingly, cancer patients are using cannabis in their efforts to manage symptoms. Studies of legal recreational cannabis suggest young adults (YA) may disproportionately account for increases in cannabis use. There are few studies of cannabis use in cancer patients and its effect on symptoms, however, and most have not stratified their results by age. To address this, we examined rates of cannabis use across three age groups: YA ages 18 to 39, adults 40 to 65, and adults older than 65 (OA). We also examined the effects of age and cannabis use on patients’ report of cancer-related symptoms. Methods: We conducted a retrospective review of 1223 cancer patients referred to outpatient supportive care for symptom management between 2014 and 2017. Patients underwent urine drug testing for tetrahydrocannabinol (THC) and completed the Edmonton Symptom Assessment Scale-Revised-CSS during their initial visit. Results: In Chi square analysis, age was significantly associated with cannabis use (p < .001): 30% of YA tested positive for THC compared to 21% of adults and 8% of OA. As a group, cannabis users reported significantly higher scores for pain, tiredness, nausea, lack of appetite, anxiety, depression, difficulty sleeping, and worse overall well-being (p values < .05). In MANOVA, there was a significant interaction effect between age and cannabis use for pain, lack of appetite, shortness of breath, anxiety, depression, difficulty sleeping, and overall well-being (p values < .05). While YA and adults who tested positive for THC reported higher symptom scores for each of these symptoms, OA patients who were THC positive reported lower scores for pain, anxiety, depression, and better overall well-being. Conclusions: Findings suggest that compared to adults and OA, more YA patients are using cannabis in attempts to control cancer-related symptoms. With the exception of OA, cannabis users rate their cancer-related symptoms as more severe than nonusers. Findings support the need for patient education about potential therapeutic benefits and adverse effects of cannabis use in cancer. Prospective, observational studies are needed to characterize patients’ use before and after a cancer diagnosis.