The aim of the present study was to analyse which histological-histomorphometric findings correspond to a radiologically diagnosed open (group I) or closed mid-palatal suture (group II) on occlusal radiographs. For this purpose, 30 radiological regions of interest (rROI) from specimens obtained from 10 subjects ranging in age from 18 to 38 years were evaluated, and compared with the suture morphology, mean sutural width, and degree of suture closure on stained sections (3/rROI). The results showed that whether or not a radiologically visible suture can be classified as 'open' depends predominantly on the main oronasal suture course in relation to the X-ray path, rather than on factors such as suture width and degree of obliteration. The mean sutural width was 231 microns in group I (n = 10 rROI) and 201 mu in group II (n = 20 rROI). The degree of obliteration in relation to the total oronasal suture length was 0.45 in group I and 1.30 per cent in group II. No significant differences were found between the corresponding parameters of the two groups. The term 'suture obliteration' or 'fusion' should be avoided if a suture is radiologically not visible, since in 11 of the 20 rROI in which the suture was not visible no obliteration was recorded morphometrically.