Background: Acne is one of the most common skin diseases. Clinical picture of acne is defined by the severity of acne. There are a lot of different treatment options available for treating acne, nevertheless isotretinoin has shown to be the most efficient one. On the other hand, isotret-inoin may lead to a wide spectrum of side effects. Aim: The aim of this retrospective study was to determine the side effects of isotretinoin in adolescents with severe acne treated between 2018 and 2021 in Children's Hospital in Zagreb, and to compare a possible correlation between side effects and age, sex and dosage of isotretinoin. Methods: Study included 117 patients aged 10 to 18 years. The research was conducted as a retrospective analysis of the database of patients receiving oral isotretinoin as a treatment for severe acne in Children's Hospital in Zagreb, in the period from 1st May 2018 to 1st May 2021. Computerized patients' medical records were used in dana collection. The data was statistically analysed in Microsoft Excel 2019 program, following the descriptive statistics methodology. Results: The statistical analysis conducted on the sample of 112 patients with severe acne showed no statistically significant relationship between categorical variables: muscle pain and male gender (p=0,692), nor between back pain and male gender (p=0,560). The results were obtained by using Chi-square test. Chi-square test did not show statistically significant relationship between muscle pain and the dosage of isotretinoin higher than 0.5 mg/kg/day (p=0,458). In the analysed group of patients, the proportion of male patients with severe acne (58,04%) was greater than female patients (41,96%). Conclusion: Cheilitis was the most common side effect of isotretinoin. In the analysed sample the proportion of male patients was greater than female. Statistically significant relationship between muscle pain and the dosage of isotretinoin higher than 0.5 mg/kg/day has not been proven (p=0,458).