Paranasal sinus osteomas are benign tumours, occasionally known to cause complications. They have a tendency to grow slowly, but the growth rate has never been evaluated previously. We retrospectively studied 44 patients with paranasal sinus osteomas. In 13 out of the 23 patients who underwent at least two sinus radiographs at different times some growth was seen. The mean growth rate of these 13 osteomas was 1.61 mm/yr, range 0.44 to 6.0 mm/yr. The endoscopic technique is a good method for the removal of osteomas and obliteration of the frontal sinus does not seem to be necessary. Two patients having osteomas with intracranial expansion are described.