Hypopituitarism in adult life is commonly acquired and the main causes are known as pituitary tumors and/or their treatments. Since there are new insights into the etiology of hypopituitarism and presence of differences in various populations, more studies regarding causes of hypopituitarism are needed to be done in different ethnic groups with sufficient number of patients. Therefore, we performed a multi-center database study in Turkish population investigating the etiology of hypopituitarism in 773 patients in tertiary care institutions. The study was designed and coordinated by the Pituitary Study Group of SEMT (The Society of Endocrinology and Metabolism of Turkey). Nineteen tertiary reference centers (14 university hospitals and 5 training hospitals) from the different regions of Turkey participated in the study. It is a cross-sectional database study, and the data were recorded for 18 months. We mainly classified the causes of hypopituitarism as pituitary tumors (due to direct effects of the pituitary tumors and/or their treatments), extra-pituitary tumors and non-tumoral causes. Mean age of 773 patients (49.8 % male, 50.2 % female) was 43.9 +/- 16.1 years (range 16-84 years). The most common etiology of pituitary dysfunction was due to non-tumoral causes (49.2 %) among all patients. However, when we analyze the causes according to gender, the most common etiology in males was pituitary tumors, but the most common etiology in females was non-tumoral causes. According to the subgroup analysis of the causes of hypopituitarism in all patients, the most common four causes of hypopituitarism which have frequencies over 10 % were as follows: nonsecretory pituitary adenomas, Sheehan's syndrome, lactotroph adenomas and idiopathic. With regard to the type of hormonal deficiencies; FSH/LH deficiency was the most common hormonal deficit (84.9 % of the patients). In 33.8 % of the patients, 4 anterior pituitary hormone deficiencies (FSH/LH, ACTH, TSH, and GH) were present. Among all patients, the most frequent cause of hypopituitarism was non-secretory pituitary adenomas. However, in female patients, present study clearly demonstrates that Sheehan's syndromeis still one of the most important causes of hypopituitarism in Turkish population. Further, population-based prospective studies need to be done to understand the prevalence and incidence of the causes of hypopituitarism in different countries.