Twenty index patients with hereditary essential tremor, and 93 first degree and 38 more distant relatives were studied at the Institute of Neurology, Queen Square, London, and Oldchurch Hospital, Romford, UK. Tremor presented in the arms. It was symmetrical in 75% and first noted in the dominant hand in 25%. In index patients, tremor spread to affect the legs, head, voice, tongue, face, and rarely the jaw. Affected relatives had tremor of the upper limbs, and spread occurred in a minority. The median age of onset for index patients was 15 yrs (range 5 - 52). The age at onset for both index and secondary cases was bimodal, peaking in the second and fifth and sixth decades. Of 14 relatives under 15 years old, 4 were described as tremulous and 2 had definite tremor, beginning as early as 2 years of age. Disability occurred in the majority but none before 15 years of age. Hunger, emotion, fatigue, and heat exacerbated tremor and disability, whereas alcohol was of benefit in 50%. Classical migraine was associated in 25% cases. Dystonia, included in some previous studies, was not encountered. Inheritance was autosomal dominant and penetrance was complete by age 65. 
COMMENT. The diagnosis should be considered in older children described as tremulous or having a mild symmetrical postural tremor of the upper limbs. Genetic counselling is pertinent in a parent with tremor and a currently unaffected child. The authors’ data show that at birth, the risk of ever developing essential tremor is 46%, and the risk of being affected by 20 years is 30%. In an unaffected child of 15 years of age, the risk of tremor by 20 years is 8%, and by 40 years, 20%.