OBJECTIVES: The aim of the study was to compare organ and effective radiation doses for collimated and non-collimated cephalometric radiographs made by a multipurpose extraoral radiation unit. METHODS: Cephalometric exposures were made from a Rando head phantom representing an average man with the Cranex Tome multipurpose radiation unit. A collimator was fabricated from a 3-mm thick piece of lead. The collimator was designed so that structures relevant for orthodontic diagnosis were not shielded, whereas the thyroid gland and the major part of the skull were shielded. Absorbed organ doses were measured using thermoluminescent dosimeters. The effective dose was calculated both with (E(sal)) and without (E) inclusion of the salivary glands. RESULTS: Use of a wedge-shaped lead collimator yielded a reduction in field size of 55% and a reduction in E from 3.0 micro Sv to 1.6 micro Sv (47%) and in E(sal) from 3.7 micro Sv to 2.2 micro Sv (41%). CONCLUSIONS: Use of a wedge-shaped collimator should be advocated in all cases where depiction of the thyroid gland and the neurocranium is not required. The resulting reduction in effective dose using our collimator was 47% (41% when the salivary glands are included), which is of clinical importance, especially in children.