Familial male-limited precocious puberty (MPP) is described in a 10year old patient with typical symptoms of the disease. Sequence analysis of genomic DNA clearly demonstrated a heterozygous T1193C transition in exon 11 of the LH receptor (LHR) gene, which results in M398T substitution in the second transmembrane helix of the protein product of this gene. The same mutation was found in the patient's mother and in her brother. The grandmother and the relatives of the patient's father were free of the mutation. The boy was successfully treated with inhibitors of steroid biosynthesis and androgen antagonists. It is suggested that this mutation caused constitutive activation of the LHR, which results in excessive formation of androgens in Leydig cells and is responsible for the symptoms of precocious puberty in this patient. This is the second case of the familial form of MPP that was maternally inherited.