Neurofibromatosis type 1 (NF1) is a genetic disease with an extremely wide range of manifestations. As yet, the individual course of NF1 cannot be predicted, and it is uncertain to what extent the disorder is associated with increased mortality. In order to gain insights into these aspects, we have conducted a 12-year follow-up study of 70 adult NF1 patients in the city of Göteborg, Sweden, whereby life expectancy, mortality, causes of death and the prognostic value of clinical findings were investigated. Clinical examinations were made, and all available records, including medical files, death certificates, and autopsy reports were scrutinized. The survival in the NF1 cohort was compared to that in the general Swedish population. Twenty-two deaths occurred in the NF1 group, whereas 5.1 deaths were expected in the general Swedish population (p = < 0.001). The mean age at death was 61.6 years. Malignancy was found in 12 (55%) of the deceased (soft tissue sarcomas in 3, and carcinomas in 9). Severe complications related to NF1 were seen in 27%. Hypertension was significantly associated with increased mortality, as 10 out of 12 (83%) patients with hypertension died during the observation period. NF1 was associated with increased mortality due to malignancy and NF1-related complications.