Objective: To evaluate differences in pain and discomfort between patients treated with clear aligners and those treated with traditional fixed orthodontic appliances. Materials and methods: 20 adult nonextraction patients were included in the fixed orthodontic appliances group (8 males, mean age 19.4 ± 4.4 years) and 20 in the clear aligners group (9 males, mean age 23.8 ± 4.4 years). Firstly, patients were asked to record their level of pain, intolerability and fatigue sensations during the first appointment (T0). Subsequently, patients were provided with a written diary to measure every day for one week (T1) their level of pain, speech difficulties, discomfort while eating, soft tissue decubitus and ulceration, difficulty in home oral hygiene, encumbrance of the tongue position and analgesic drugs consumption. The same diary was provided again after the adjustment appointment (T2). The data collected at T0 were analysed by means of an independent sample t test. For the remaining data, a two-way ANOVA was conducted. Sidak multiple comparison test was performed to compare the two groups at each time point. The level of significance was set at P 0.05. Results: Patients in the fixed orthodontic appliances group reported significantly more pain and intolerability at T0 (P = 0.035). Discomfort while eating, soft tissue decubitus and ulceration and home oral hygiene were statistically significantly lower in the clear aligners group at T1 than at T2. Conclusions: Therapy with traditional fixed orthodontic appliance caused more discomfort to the patients, as compared to clear aligner therapy. Keywords: brackets, clear aligners, orthodontic appliances