Separating Parkinson's disease from the various causes of atypical parkinsonism (AP) is a common and clinically relevant challenge in clinical practice. Distinguishing between the different causes of AP is even more difficult. Here the authors discuss a systematic, clinically based and three-pronged approach that can assist clinicians in establishing the correct diagnosis in the consulting room. The three consecutive steps include: (1) to verify that the clinical syndrome truly represents parkinsonism (hypokinetic-rigid syndrome); (2) to search systematically for 'red flags' (alarm signs that may signal the presence of AP); and (3) to integrate these two steps, as a basis for a narrow differential diagnosis and a guide for further ancillary tests.