Background: This article describes the growth rate of pituitary adenomas, their invasion and potential recurrence. Some of them grow rapidly while others remain in a dormant condition for a long time. The recurrence rate is also very hard to forecast. The pituitary adenomas that initially reduced their proliferation rate now acquire a rapid one, producing aggressive recurrences. Materials and methods: Eighty two cases of pituitary adenomas were studied. The classification of human pituitary adenomas has been profoundly assisted by immunohistochemistry. Ki-67 antibody was used to assess the proliferative index of pituitary adenomas. Results: Acidophil type adenomas or acidophil cells areas within mixed pituitary adenomas had the highest proliferation rate. Chromophobe pituitary adenomas were Ki67 negative in 90%, as well as the ones that presented the basophilic cells. The pituitary adenomas with a trabecular growth pattern had the lowest rate of proliferation, in about 50% of the cases being zero. The heterogeneity expression of growth factors and corresponding receptors is dependent on hormonal profile of pituitary adenomas. Conclusion: The pituitary adenomas proliferation rate depends on the type of secreted hormone as well as on the hormonal associations met in some cases of pituitary adenomas.