The presenting features and their subsequent evolution in 36 patients with pathologically proven or clinically probable corticobasal degeneration are described. The most common initial complaint was of a unilateral 'clumsy, stiff or jerky arm' (n = 20). Typically the arm was akinetic, rigid and apraxic. In about a third of these the arm was held in a striking and characteristic fixed dystonic posture. Jerking of the arm, due to action and stimulus-sensitive myoclonus accompanied these symptoms in about a third of the cases. The next most common presentation (n = 10) was difficulty walking due to clumsiness and loss of fine motor control of one leg due to apraxia or dysequilibrium, or a combination of both. Sensory symptoms in the affected arm heralded the onset of illness in three and accompanied a motor disturbance in two cases. Presentation with dysarthria or a behavioural syndrome were rare. The symptoms progressed slowly, usually involving first the ipsilateral arm and leg, but gradually spread to affect all four limbs. After a mean follow-up of 5.2 years (range 2-8 years) gait difficulties and a supranuclear ophthalmoplegia had emerged in most patients and dysarthria and pyramidal signs were common. Higher mental function was relatively preserved in most and a cortical sensory loss was evident in a quarter of cases.