Since 1994, a population-based study of frontotemporal dementia (FTD) in The Netherlands has aimed to ascertain all patients with FTD, and first prevalence estimates based on 74 patients were reported in 1998. Here, we present new prevalence estimates after expansion of our FTD population to 245 patients, with emphasis on the prevalence in the province Zuid-Holland where the main study centre is located. All neurologists and physicians in nursing homes received a yearly postal enquiry about suspected FTD cases. FTD was diagnosed in 245 patients according to the Lund-Manchester criteria, supported by neuroimaging and neuropsychology. tau mutation analysis was performed in a subgroup of 154 patients (63%), and 40 out of 98 patients (41%) who died during follow-up were autopsied during the course of the study. The prevalence of FTD in the province Zuid-Holland was 3.6 per 100,000 at age 50-59 years, 9.4 per 100,000 at age 60-69 years and 3.8 per 100,000 at age 70-79 years. The median age at onset of the 245 patients (51% female) was 58.0 years (range 33-80 years). Dementia in one or more first-degree family members was found in 43% of patients and mutation analysis of the tau gene showed mutations in 34 patients (19 P301L, five L315R, four G272V, four R406W, one Delta K280 and one S320F), all with a positive family history for dementia (14% of the total population, 32% of patients with a positive family history). Pathological findings in the 40 autopsied patients consisted of dementia lacking distinctive histology in 22%, FTD with ubiquitin-positive inclusions in 33%, Pick's disease in 15% and tauopathy in the remaining 30% of patients, with tau mutations identified in more than half of the latter patients. We conclude that the prevalence of FTD in The Netherlands is higher than previously reported, confirming that FTD is more common than was previously thought. The finding of tau mutations in 32% of patients with a positive family history for dementia justifies mutation screening in FTD patients with a positive family history, while tau mutations in non-familiar cases are rare.