The presence of bilateral arm tremor is a key diagnostic feature of essential tremor (ET). We analyzed the presence of unilateral arm tremor in familial ET cohort of 133 autosomal dominant ET kindreds with 412 affected individuals. Inclusion criteria in patients with unilateral arm postural and/or kinetic tremor required the duration of tremor for at least 5 years, without hypokinetic-rigid syndrome, dystonic posturing, or history of sudden onset of tremor. Only subjects with at least one living first degree relative who met diagnostic criteria for definite ET were included. Eighteen subjects met the inclusion criteria and five had postural tremor only, while the majority (13/18) had a combination of postural and kinetic tremor. Our data shows that unilateral tremor associated with ET is relatively rare and can be identified in 4.4% patients in a cohort of familial ET.