Object: To present population-based and age related incidence of surgery and clinical outcome for adult patients operated for hydrocephalus, registered in the Swedish Hydrocephalus Quality Registry (SHQR). Methods: All patients registered in SHQR during 2004-2011 were included. Data on age, gender, type of hydrocephalus and type of surgery were extracted as well as three months outcome for patients with idiopathic normal pressure hydrocephalus (iNPH). Results: The material consisted of 2360 patients, 1229 men and 1131 women, age 63.8 +/- 14.4 years (mean standard deviation (SD)). The mean total incidence of surgery was 5.1 +/- 0.9 surgeries/100,000/year; 4.7 +/- 0.9 shunt surgeries and 0.4 +/- 0.1 endoscopic third ventriculostomies. For iNPH, secondary communicating hydrocephalus and obstructive hydrocephalus, the incidence of surgery was 2.2 +/- 0.8, 1.9 +/- 0.3 and 0.8 +/- 0.1/100,000/year, respectively. During 2004-2011, the incidence of surgery increased in total (p = .044), especially in age groups 70-79 years and amp;gt; 80 years (p = .012 and p = .031). After surgery, 253 of 652 iNPH patients (38.8%) improved at least one step on the modified Rankin scale (mRS). Number needed to treat was 3.0 for improving one patient from unfavourable (mRS 3-5) to favourable (mRS 0-2). The mean score of a modified iNPH scale increased from 54 +/- 23 preoperatively to 63 +/- 25 postoperatively (p amp;lt; .0001, n = 704), and 58% improved. No significant regional differences in incidence, surgical techniques or outcome were found. Conclusions: Incidence of hydrocephalus surgery increased significantly during 2004-2011, specifically in elderly patients. Surgical treatment of INPH markedly improved functional independence, but the improvement rate was low compared to recent single- and multicentre studies. Thus, the potential for surgical improvement is likely lower than generally reported when treating patients as part of everyday clinical care.