Neurofibromatosis 1 (NF1) is a neurocutaneous‐skeletal disorder often accompanied with varying degrees of cognitive and motor problems that potentially affect speech and language. While previous studies have shown that NF1 may be associated with a variety of deviations in the patients' speech, they have not investigated the characteristics in phonetic detail. Our clinical observation that many patients share a distinct voice and manner of speaking led to the primary aim of this study, which was to present a comprehensive description of speech in NF1. A total of 62 patients with NF1 (age range 7–66 years), and a control group of 24 speakers (age range 7–62 years) were evaluated for their speech. The test sessions were recorded and the data were analyzed both by ear and by acoustic measurements. The data were analyzed separately by two trained phoneticians, and a summary was produced after comparing the two independent analyses. Various speech problems were observed among patients with NF1. Individual variation was remarkable, but the deviations were more common and severe in children than in adult patients. In addition, men with NF1 had more speech deviations than women with NF1. Findings include deviations in voice quality, problems in regulating pitch, deviant nasality, misarticulation, and disfluency. We suggest that difficulties in speech, particularly in regulating pitch, may have negative social implications. Our results highlight which components of speech require particular attention in speech therapy for patients with NF1. © 2009 Wiley‐Liss, Inc.