Purpose: The incidence of neurofibromatosis 1 (NF1) is ~1/2,000 live births, but the current estimates of prevalence vary greatly. This retrospective total-population study was aimed at determining the prevalence of NF1 in Finland.

Methods: All secondary and tertiary referral centers of Finland were searched for NF1 patients. Patient records were manually reviewed and patients fulfilling the National Institutes of Health diagnostic criteria for NF1 were included. Prevalence on 31 December 2005 was determined. Data on incidence and survival were combined to refine the prevalence estimation.

Results: A total of 1,279 patients with NF1 were alive on 31 December 2005, yielding a prevalence of 1/4,088 (95% confidence interval (CI) 1/4,320–1/3,869). The survival of patients with NF1 was inferior compared with the general population (hazard ratio 3.10, 95% CI 2.73–3.53, P < 0.001). When the survival rates of NF1 patients and the Finnish population were combined with an estimate of NF1 incidence, a prevalence of 1/2,052 (95% CI 1/2,176–1/1,941) was estimated for NF1 in a population aged 0–74 years.

Conclusion: NF1 is a much more common disorder than previously thought. A large proportion of NF1 patients may not be correctly identified by health-care systems or they do not seek secondary health care for their NF1.