Precocious puberty (PP) and intellectual handicap were present in 3 males in 2 generations of a Western Australian family. The 2 obligate carrier women were of normal intelligence but were grossly obese; one died of a cardiomyopathy at 55 years. The youngest affected male was found to have PP at 3 years. His mother was then pregnant, and because of her family history, was aware of the risk to have an affected male. Her mother had given birth to 2 sons with PP. By school age both of these males were mildly intellectually handicapped and this later became moderate. Apart from these 3 affected males, the 2 carriers lost 6 of their other 8 offspring, leaving only one normal woman and her unaffected son. The Fragile X test was negative on all males. This appears to be a new X-linked mental retardation syndrome, and a condition different from true idiopathic PP, or familial PP affecting both sexes, or PP with X-linked dominant inheritance.