Previous case reports and retrospective studies suggest that pituitary dysfunction may occur after acute bacterial or viral meningitis. In this prospective study we assessed the pituitary functions, lipid profile and anthropometric measures in adults with acute bacterial or viral meningitis. Moreover, in order to investigate whether autoimmune mechanisms could play a role in the pathogenesis of acute meningitis-induced hypopituitarism we also investigated the anti-pituitary antibodies (APA) and anti-hypothalamus antibodies (AHA) prospectively. Sixteen patients (10 males, 6 females; mean +/- A SD age 40.9 +/- A 15.9) with acute infectious meningitis were included and the patients were evaluated in the acute phase, and at 6 and 12 months after the acute meningitis. In the acute phase 18.7% of the patients had GH deficiency, 12.5% had ACTH and FSH/LH deficiencies. At 12 months after acute meningitis 6 of 14 patients (42.8%) had GH deficiency, 1 of 14 patients (7.1%) had ACTH and FSH/LH deficiencies. Two of 14 patients (14.3%) had combined hormone deficiencies and four patients (28.6%) had isolated hormone deficiencies at 12 months. Four of 9 (44.4%) hormone deficiencies at 6 months were recovered at 12 months, and 3 of 8 (37.5%) hormone deficiencies at 12 months were new-onset hormone deficiencies. At 12 months there were significant negative correlations between IGF-I level vs. LDL-C, and IGF-I level vs. total cholesterol. The frequency of AHA and APA positivity was substantially high, ranging from 35 to 50% of the patients throughout the 12 months period. However there were no significant correlations between AHA or APA positivity and hypopituitarism. The risk of hypopituitarism, GH deficiency in particular, is substantially high in the acute phase, after 6 and 12 months of the acute infectious meningitis. Moreover we found that 6th month after meningitis is too early to make a decision for pituitary dysfunction and these patients should be screened for at least 12 months. In addition, the occurrence of AHA and APA positivity due to acute infectious meningitis was demonstrated for the first time. Further longer-term prospective investigations need to be carried out on a larger cohort of patients to understand the role of autoimmunity in the pathogenesis of late hypopituitarism after acute infectious meningitis.