One of the most common sites for the compartment syndrome (CS) is the forearm. Its compartments have been studied by injection of colored gelatin into the particular anatomical spaces. The three "pressure-measuring-points" recommended in the clinical literature to measure intracompartmental tissue pressure in equivocal diagnostic cases were used for the dye injections on the forearms of five preserved cadavers of adults. However, instead of the compartments especially affected in CS two adjacent spaces were revealed. In order to elucidate the clinical relevant spaces two additional approaches for the injection had been used. Cross-sections at 15 mm intervals of the injected forearms had been performed. Some of them are presented and schematically summarized in this article. Recent studies have suggested that there are different guidelines for description of the anatomically isolated spaces. However, especially one of these spaces seems to be responsible for the CS on the forearm. The remarkable features of this so called "deep flexor compartment" are its very restrictive envelopes, its rare fascial contacts, its impermeable seal in proximal-radial direction as well as the extremely endangered structures within the compartment. The flexor carpi ulnaris muscle is recommended to be the "primary structure" for measuring the tissue pressure as well as for surgical decompression. The article reviews the anatomical base of the CS.