Literature data about the reaction of arylglyoxals with  thiourea has been discussed. It has been shown that no systematic studies in this issue had ever been carried out, furthermore some data is contradictory. The reaction of arylglyoxals with thiourea is reported to be a stepwise process that depends on at least two factors. It is reaction conditions such as temperature and solvent. Also the nature of glyoxal may have crucial influence on the structure of products. In this article has been provided the convincing evidence of formation three different kinds of heterocyclic systems upon reaction of p-substituted phenylglyoxals with N-methyl and N-phenylthiourea.