We studied the rate of initial "misdiagnosis', along with factors than might distinguish such patients, in 64 patients with amyotrophic lateral sclerosis (ALS) who completed a survey of 34 questions. Announcement of the survey was made by electronic newsletter and users group bulletin board directed at ALS patients. The questionnaire was distributed to interested ALS patients via electronic mail (e-mail), and 64 ALS patients (81% from the USA) returned their completed questionnaires via reply e-mail or postal mail. Seventeen patients (27% of total group) indicated at least 1 prior misdiagnosis, most commonly spinal stenosis/radiculopathy; 5 listed unnecessary and costly surgical treatments (laminectomy, endarterectomy). Misdiagnosis appeared to be more common in patients above age 60 and may be more common in patients originating in cities versus smaller communities. Mean time from onset of first symptom until definitive diagnosis of ALS was prolonged in patients with initial misdiagnosis (19 months) compared with non-misdiagnosed patients (10 months). Such a previous misdiagnosis may decrease a patient's chance of acceptance into multicenter ALS drug trials.