Norway lobster, Nephrops norvegicus, has a hard exoskeleton, and also an endoskeleton, i.e. a gastric mill, which is fused with the stomach membrane and consists of three structures: mesocardial, zygocardial and pterocardiac teeth. The mesocardial tooth and its morphometric characteristics are the subject of this research. Norway lobster is inhabiting channel areas of the Northern and Central Adriatic, and the open Adriatic Sea, where it is exploited by bottom trawl nets and creels. The aim of this study was to explore the differences of mesocardial tooth length and width, carapace length and width between the sexes and between samples from different fishing grounds in the Adriatic Sea. A positive correlation was found for all sampled individuals between mesocardial tooth width and length, carapace width and length, mesocardial tooth length and carapace length and mesocardial tooth width and carapace width, except for the samples from Moščenička Draga where the growth of the mesocardial tooth of the shrimp is not conditioned by the growth of the carapace length. The difference in length parameters was found between males and females, between samples from different fishing grounds and also between samples fished with different fishing gears, except in samples from Moščenička Draga. The average length of the mesocardial tooth for males inhabiting the channel area was 2.83±0.29 mm, for females 2.79±0.35 mm, and for males and females inhabiting the open sea 2.38±0.36 mm and 2.24±0.41 mm, respectively. The results of this thesis can be the basis for further research of morphological characteristics of Norway lobster, and can lead to a better understanding of the influence of ecological factors and fishing gears on the growth and development of the Norway lobster endoskeleton.