An 11-year-old girl was evaluated for walking difficulties and fatigue at the end of the day in the last 2 years. Handwriting was also difficult with 'cramps' after a short time of writing. Neurological examination was normal most of the time but in the evening and after exercise, an abnormal walking posture and rare dystonic movements of the foot could sometimes be seen. The mother was found to have mild parkinsonism and is asymptomatic on L-dopa. In the daughter, all symptoms and signs disappeared on L-dopa, but returned when the drug was withdrawn. The changes on- and off-treatment were documented with videofilms and computerized analysis of writing samples. The situation has been stable during a 5-year follow-up. We draw attention to this 'forme fruste' of dopa-sensitive childhood dystonia which becomes manifest with exercise and which can easily go unrecognized. We also discuss and illustrate the methods used for the analysis of writing.