The ABC method is a basic and simplified form of behavioural modification therapy for use by nurses. ABC refers to the identification of Antecedent events, target Behaviours, and Consequent events. A single-case experimental AB design was used to evaluate the effects of the ABC method on a woman diagnosed with olivo-ponto-cerebellar ataxia. Target behaviour was verbal aggressive behaviour during ADL care, assessed at 9 time points immediately before implementation of the ABC method and at 36 time points after implementation. A randomisation test showed a significant treatment effect between the baseline and intervention phases (t = .58, p = .03; ES [Nonoverlap All Pairs] = .62). Visual analysis, however, showed that the target behaviour was still present after implementation of the method and that on some days the nurses even judged the behaviour to be more severe than at baseline. Although the target behaviour was still present after treatment, the ABC method seems to be a promising tool for decreasing problem behaviour in patients with acquired brain injury. It is worth investigating the effects of this method in future studies. When interpreting single-subject data, both visual inspection and statistical analysis are needed to determine whether treatment is effective and whether the effects lead to clinically desirable results.