A new series of equations is presented for predicting the adult height of a child given present height and bone age. These equations (TW height prediction, Mark II) which replace the ones given in 1975 (TW height prediction, Mark I) are based on larger numbers of normal children, and more importantly on a sample that includes, for the first time, numbers of very tall, very short, and very growth-delayed children. In addition, equations are given for use when the increment of height or bone age, or both, over the previous year is known. These variates improve the prediction at most ages over 8 years in girls and 11 years in boys. The previously given parental allowance has been dropped. Typically 95% of the predictions lie within +/- 8 cm of the real value for boys aged 10 years, falling to +/- 6 cm for boys aged 15 years, or +/- 4 cm if their previous height increment is known. For premenarcheal girls the predictions lie within about +/- 6 cm at age 8 years; a figure which diminishes little till 13 years unless height and bone age increments are known, when it reaches +/- 4 cm at 13 years. For postmenarcheal girls the predictions are substantially more accurate.