The Tanner-Whitehouse method of assessing skeletal maturity has been in use for more than three decades. Problems in assigning bone ages arise from many sources. The most significant sources of error are poor positioning of the hand when the radiograph is taken, which alters the radiographic appearance of the epiphysis and makes interpretation unnecessarily difficult, and the lack of consistency in repeat ratings of the same film by one or more observers (intra- and inter-observer error). In addition, use of the system outside the limits of its design is a common error seen in clinical practice. Computer systems are now being developed with the aim of reducing many of the inconsistencies associated with radiographic investigations of normal children.