Tremor in Klinefelter's syndrome is believed to be essential tremor since the publication of "Klinefelter's syndrome and essential tremor" in 1969. However, the author also stated that tremor in Klinefelter's syndrome might differ from essential tremor. A 71-year-old man with Klinefelter's syndrome who suffers from postural hand tremor is described. The electromyogram indicated lower motor neuron disturbance and chronic neurogenic change. The muscle biopsy indicated neurogenic muscle atrophy. Upon testosterone administration, the amplitude of tremor was reduced and a gradual improvement in handwriting was observed. The tremor in this patient was different from essential tremor. The foresight by Baughman in 1969 proved to be true in this patient. This case report provides new insights into the pathogenesis and treatment of tremor in Klinefelter's syndrome, which would benefit patients who suffer from the tremor.