Patients presenting with essential tremor who later develop Parkinson’s disease (PD) are recalled by most practising neurologists, but there remains debate around the relationship of the two diagnoses. In this issue the paper by Chaudhuri et al(pp 115) reports long term clinical follow-up of patients with asymmetric or unilateral postural tremor, where the diagnosis evolved from essential tremor to PD. The case against coincidental dual diagnosis is well argued, but ascertainment bias limits application of the conclusions to prospective patient management. Selected patients in their series had abnormal presynaptic dopaminergic single photon emission computed tomography (SPECT) imaging …