Acne vulgaris is one of the most common dermatological diseases. The prevalence may be as high as 83-95% at age 16, but decreases at age 20, and is very low at age 35. The aetiology and pathogenesis are not completely known, but the following factors are involved: 1) increased sebum secretion, 2) follicular keratinisation, 3) bacteria and 4) inflammation. Furthermore, genetic and exogenic factors play a role. Acne can be divided into 5 groups depending on its severity. Treatment principles within these 5 groups are reviewed. Treatment can not be expected to take effect before 1-2 months have passed, but all patients can be cured with the right treatment. The effects and side effects of the various treatments are described. Treatment with isotretinoin should only be initiated by dermatologists.