To compare clinical parameters of patients treated with botulinum toxin type A (BTX) for treatment of idiopathic cervical dystonia (ICD) and for tardive cervical dystonia (TCD), we studied 156 patients (149 with ICD and 7 with TCD) who were treated with serial injections of BTX over 5 years. We hypothesized that patients with TCD and ICD would demonstrate similar improvement in severity scores after treatment with BTX. The diagnosis, dates, dosages, and frequency of BTX injected and severity assessments were recorded into a computerized database. Nonparametric Wilcoxon rank sum and signed-rank tests were used to assess statistical significance. The change in severity scores between the first treatment and last treatment in both groups was not statistically significant (p = 0.4859), indicating similar improvement. The difference in BTX doses was significant (p = 0.0045). ICD patients (n = 149) received an average of 219.8 +/- 63.5 units and those with TCD (n = 7) were treated with an average dose of 287.4 +/- 60.3 units. The average number of days between treatments for individuals with ICD was 142.9 +/- 85.8, similar to that for persons with TCD (144.7 +/- 64.5) (p = 0.6075). Our analysis provides preliminary evidence that the improvement from the administration of BTX for patients with ICD and TCD is similar.