Purpose: Previous reports have described panhypopituitarism associated with severe cases of hemorrhagic fever with renal syndrome (HFRS), but the prevalence of hormonal deficiencies after nephropathia epidemica (NE), a milder form of HFRS, has not been studied. This study was conducted to determine the prevalence of hormonal defects in patients with acute NE and during long-term follow-up. Methods: Fifty-four patients with serologically confirmed acute NE were examined by serum hormonal measurements during the acute NE, after 3 months, and after 1 to 10 (median 5) years. Results: Thirty out of 54 (56%) patients had abnormalities of the gonadal and/or thyroid axis during the acute NE. After a median follow-up of 5 years, 9 (17%) patients were diagnosed with a chronic, overt hormonal deficit: hypopituitarism was found in 5 patients and primary hypothyroidism in 5. In addition, chronic subclinical testicular failure was found in 5 men. High creatinine levels and inflammatory markers during NE associated with the acute central hormone deficiencies, but not with the chronic ones. Conclusions: Hormonal defects are common during acute NE and surprisingly many patients develop chronic hormonal deficiencies after NE. The occurrence of long-term hormonal defects cannot be predicted by the severity of acute NE. According to the reviewer's advice, we have now added two new tables (Tables 3 and 4) to clarify the presentation of the observations. Table 3 shows the clinical diagnoses and serial plasma hormone levels in those 9 NE patients who presented with chronic, overt hormonal deficits. In Table 4, we show the acute-phase clinical and laboratory findings of the 9 patients, who developed chronic hormonal defects after NE, compared to those 45 patients, whose hormone levels remained normal during the follow-up. Since the clinical diagnoses of hormonal deficiencies are now shown in Table 3 (in the revised version), we have omitted the corresponding text from Results, Hormonal deficiencies: "Of these 9 patients, 2 were diagnosed with isolated central hypogonadism, 2 had multiple pituitary hormone deficiencies, 2 had primary hypothyroidism only, one had primary hypothyroidism and primary hypogonadism, one was diagnosed with isolated central hypogonadism and peripheral hypothyroidism, and one with primary hypothyroidism and a possible GH deficiency (undetectable GH level and IGF-1 6.5 nmol/l; reference range 10-29 nmol/l)." In order to further clarify the results, we have also referred to the patients described in Table 3 (e.g. "patient 1, table 3") in the revised text: Results, page 8, Hormonal deficiencies, lines 6 and 12, as well as in Results, Imaging studies, page 9, the first and the third line). We have omitted the following text from Results, Imaging studies: "Testo 11.6-10.8-8.1-7.4 nmol/l, LH 1.6-1.4-2.0-2.6 U/l, fT4 12.5-11.8-10.4-10.4 pmol/l, and TSH 1.2-1.1-1.0-0.9 mU/l, measured in the acute phase, and after 1 year, 5 and 9 years, respectively", since the same values are now shown in Table 3 (patient 2) o...