152 sinuses of children with acute maxillary sinusitis were roentgenographically examined with both a standard occipito-mental (OM) and an occipito-mental side (OMS) projection. In the acute phase of the disease the OMS projection was superior in 13% of sinuses in demonstrating the presence of retained maxillary secretion. When the result of medical treatment was controlled after two weeks the superiority was seen only in 1% of sinuses due to the major difference between the subgroups' 'mucosal thickening'. The clinical importance of the OM finding 'mucosal thickening' seems to be different in the acute and in the follow-up phase. From the clinical point of view single OM projection seems to be sufficient in most cases. However, the OMS projection seems to be a useful adjunct to or replacement of the standard OM radiogram in the acute phase of childhood maxillary sinusitis, if it is felt necessary to demonstrate the presence of retained secretion in spite of the increased radiation. When the result of treatment is evaluated, in unilateral cases OMS projection can replace OM projection.