Acne inversa (formerly: hidradenitis suppurativa, pyoderma fistulans sinifica) is a chronical-suppurative and scarring disease with predilection in the apocrine gland bearing areas (intertrigines). Hyperkeratosis of the terminal hair follicle is to be considered initial in pathogenesis. Aim of this thesis was the histomorphological description of the disease, the chronological classification of these characteristics into the overall process as well as the capture of preferably very early morphological changes. Methods: Operative material from 60 patients (= 262 preparations) with partly persistent acne inversa were investigated histologically. Additionally, patient related clinical data was evaluated. Results: Acne inversa is a disease of the adolescence. An above-average long duration of the disease (9.4 years) up to a curative therapy (surgery) and a consecutive affection of multiple areas within its progress can be regarded as critical. Smoking seems to play an important role as trigger- and realization-factor respectively. On a histological level, besides the well-known terminal hair follicle hyperkeratosis, there are localised lymphocytical inflammatory cells which are of importance in the initial morphogenesis. What is impressive, is a follicle-associated (perifollicular, infrainfundibular) inflammatory mixed infiltrate (CD-3, CD-4, CD-8, CD-68, CD-79, CD-4/CD-8-ratio: 2:1), here a selective CD-8-cell-epitheliotropism is striking. The consequences of the further progress of the disease are the rupture of the terminal hair follicle and the spreading of the inflammation into the surrounding tissue. It has to be considered that the inflammation firstly spreads dermal horizontally. An involvement of the subcutis seems not apparent. A psoriasiform epidermal hyperplasia (58% of the patients) is another and uncommon histological finding. Here an association with an inflammatory infiltrate is also existant, the composition is comparable to the follicular infiltrate (CD-4/CD-8-ratio: 1.5:1) and a selective CD-8-cell-epidermotropism is shown as well. In the conclusion, future aims are to investigate to what extent inflammatory (initial) infiltrates induce on the one hand, hyperkeratosis at terminal hair follicles and on the other hand, epidermal psoriasiform hyperplasia. Such cytological findings could establish new therapy options (medicamentous) and used at an early stage, they could save the patient from a persistent suffering.