An autosomal dominantly inherited defect in the GCH1 gene that encodes guanosine triphosphate cyclohydrolase 1 (GTPCH1) is the most common cause of dopa-responsive dystonia (DRD). A classic phenotype of young-onset lower limb dystonia, diurnal fluctuations, and excellent response to levodopa has been well recognized in association with GCH1 mutations, and rare atypical presentations have been reported. However, a number of clinical issues remain unresolved including phenotypic variability, long-term response to levodopa and associated non-motor symptoms, and there are limited data on long-term follow up of genetically proven cases. We present a detailed clinical evaluation of 34 patients (19 women, 15 men) with confirmed mutations in the GCH1 gene. We found that the classic phenotype was most frequent (n=23), with female predominance (F:M=16:7), and early onset (mean 4.5 years) with involvement of legs. However, a surprisingly large number of patients developed craniocervical dystonia, with spasmodic dysphonia being the predominant symptom in two subjects. A subset of patients, mainly men, presented with either a young-onset (mean 6.8 years) mild DRD variant not requiring treatment (n=4), or with an adult-onset (mean 37 years) Parkinson’s disease-like phenotype (n=4). Two siblings were severely affected with early hypotonia and delay in motor development, associated with compound heterozygous GCH1 gene mutations. We also describe a number of supplementary features including restless legs-like symptoms, influence of female sex hormones, predominance of tremor or parkinsonism in adult-onset cases, initial reverse reaction to levodopa, recurrent episodes of depressive disorder, and specific levodopa-resistant symptoms (writer’s cramp, dysphonia, truncal dystonia). We report that levodopa was used effectively and safely in 20 pregnancies, and did not cause any foetal abnormalities.