Nimesulide is a quite popular non-steroidal anti-inflammatory drug (NSAID), which has been demonstrated to preferentially inhibit cycloxygenase-2 (COX-2), thus exerting milder gastrointestinal and renal side effects. Apart from the original products (Aulin and Mesulid), several copy and generic nimesulide-containing preparations are presently available on the Italian market. Generics are defined by the World Health Organization (WHO) as interchangeable multi-source pharmaceutical products and, according to international regulatory issues, their bioequivalence to an already marketed reference product has to be proven. Due to its physico-chemical properties, and in particular to the low solubility, nimesulide appears to be a critical molecule from a biopharmaceutical point of view. On the basis of these premises, the aim of the present work was to perform a comparative evaluation of tablets in vitro behaviour for the best-selling copy (Sulidamor) and generic (Nimesulide Dorom) in reference to the original products. The results provided by the dissolution test pointed out statistically significant differences in the in vitro behaviour displayed by the original products on one hand and by the copy as well as generic preparations in exam on the other.