Some plants that are processed into foods often contain natural substances that may be hazardous to human health. One example is coumarin, which is known to cause liver and kidney damage in rats, mice and probably humans. The main source of coumarin in the diet is cinnamon. The name 'cinnamon' is correctly used to refer to Ceylon cinnamon, also known as 'true cinnamon'. However, other plant species are sometimes sold with the label of cinnamon. This is the case of Cinnamomun aromaticum (cassia). In recent years, due to its cheaper price, cassia is replacing true cinnamon in the European food market being largely used in the preparation of some kinds of sweets. Several European health agencies have recently warned against consuming high amounts of cassia due to its high content of coumarin. In this study, 34 samples of cinnamon and 50 samples of cinnamon-containing foodstuffs were collected from the Italian market. Quantitative determinations of coumarin and cinnamaldehyde were performed by high-performance liquid chromatography (HPLC) with diode array detector (DAD). The analytical method was in-house validated assessing recovery, repeatability, linearity, limit of detection (LOD) and limit of quantitation (LOQ). The results showed that about 51% of cinnamon samples consisted of cassia, 10% were probably a blend of cassia and Ceylon cinnamon, whereas only 39% were actually Ceylon cinnamon. As far as cinnamon-containing foods are concerned, the samples often exceeded the maximum level fixed in the European Flavourings Directive of 2 mg kg(-1).