BACKGROUND : Pilonidal sinus disease (PSD) is a simple chronic inflammatory condition resulting from loose hairs forcibly inserted into vulnerable tissue in the natal cleft. It is an acquired disease with a slight familial tendency. There is no agreement on optimum treatment and the multitude of therapeutic options cannot be compared due to the lack of a universally adopted classification of the disease. The aim of our study was to perform a systematic review of the literature to determine how presentations of PSD are classified and reported. METHODS : A systematic review of the English language literature was undertaken searching studies published after 1980. RESULTS : Eight classification systems of PSD were identified. Most classification systems were based on anatomical pathology hypotheses. The location and number of sinuses were the main factors defining classification systems. No articles were retrieved that assessed the validity and/or reliability of the classification system employed. Furthermore, there was no evidence to suggest a correlation between prognosis outcome and subgroup. CONCLUSIONS : Based on the evidence available from the literature reviewed we have no recommendations regarding the use of the current classification of PSD. A well-recognised and practical classification system to guide clinical practice is required.