Purpose: Patients undergoing cholecystectomy report experiencing stress related to the surgery, complaining of pain and poor sleep quality. Aromatherapy is known to have positive effects on these complaints. However, the effect of aromatherapy on cholecystectomy patients has yet to be determined. The aim of this study, therefore, was to investigate the effects of aromatherapy on laparoscopic cholecystectomy patients' stress, pain, and sleep quality. Methods: This study was a randomized controlled trial involving 69 adults who underwent laparoscopic cholecystectomy. Essential oil therapy was given to an intervention group, and almond oil was given to a placebo group. The outcome variables were stress, pain, and sleep quality. Results: There were no differences between the groups in terms of demographic and clinical characteristics and pretreatment dependent variables. After the intervention, subjective stress (F ¼ 7.43, p < .001), objective stress (F ¼ 2.70, p ¼ .034), parasympathetic nerve activity (F ¼ 2.65, p ¼ .036), pain (F ¼ 8.74, p < .001), analgesics administration (F ¼ 22.43, p < .001), and sleep quality (F ¼ 5.23, p < .001) were significantly different between the intervention, placebo, and control groups. Sympathetic nerve activity was not significantly different. The effect sizes regarding the sleep quality of the intervention versus control group and the intervention versus placebo group were 1.92 and 1.52, respectively. Conclusion: Postoperative aromatherapy received by cholecystectomy patients was effective in reducing stress and pain and improving sleep quality. No side effects of aromatherapy were reported during the experimental treatment.