Background/aim Needle phobia occurs in more than half of diabetic patients due to the pain caused by frequent insulin injections. Therefore, this study evaluated the effect of topically administered lavender aromatherapy on the pain of insulin injections in diabetic patients. Materials and methods In this double-blind randomized controlled and experimental study, patients who met the study criteria were divided into three groups; topical lavender oil (n = 60), placebo (n = 60), and control (n = 60) groups. The data were collected using the “Patient Information Form”, the “Follow-up Form”, the “Verbal Category Scale (VCS)”, and the “Visual Analogue Scale (VAS)”. Results The results revealed no significant difference between the patients in the topical lavender oil group before and during the insulin injection in terms of VAS and VCS pain scores (p > 0.05). In the placebo and control groups, the mean VAS and VCS pain scores during insulin injection were found to be significantly higher than before insulin injection (p < 0.05). Besides, the mean VAS and VCS scores during insulin injection were significantly higher in the placebo and control groups than the topical lavender oil group (p < 0.05). Conclusion The study showed that patients who were administered topical lavender oil felt less pain after insulin injection than those in the placebo and control groups. Therefore, topically applied lavender aromatherapy can be easily used for pain control in insulin-dependent diabetic patients (clinical trial number NCT04767737).