Introduction: The periaqueductal gray matter is classically divided into four major nuclei: dorsal, medial, lateral and ventral, according to their cytoarchitectural feature. While some studies indicate that these nuclei are composed of similar cell types, there is some evidence that each of these nuclei is arranged in discrete groups of cells on the basis of their neuronal morphology and their afferent and efferent connection. Materials and Methods: The neurons were labelled by Golgi staining from five human midbrains, obtained from medico-legal forensic autopsies of adult human bodies and free of significant brain pathology. Two-dimensional digital images of each periaqueductal gray neuron were recorded by a digital camera connected to a light microscope. Results: The neurons of the periaqueductal gray were qualitatively analysed, and these cells were classified into two main classes. Taking into account the shape of the cell body, numbers of the primary dendrites, shape of the dendritic tree and their position within the periaqueductal gray, three subclasses of the large neurons and two subclasses of the small neurons have been recognized. Conclusion: The present study supports the hypothesis that the periaqueductal gray matter could be subdivided into discrete cell groups according to their neuronal morphology.