Oto-rhino-laryngologists usually deny the existence of infant chronic ethmoido-maxillary sinusitis, generally agreeing that the earliest signs of pneumatization of the maxillary sinuses cannot be observed earlier than 18 months of age. Based upon ten cases we present evidence that this notion of "late sinusal pneumatization" should be re-examined, pneumatized maxillary sinuses being possible as early as 11 months of age. Thus, at that age, radiodiagnosed apneumatosis which is considered as physiological, may express various conditions, such as true anatomical apneumatosis, chronic glue sinusitis, or simple inflammatory sinusitis of the mucous membrane. Because it is impossible to clinically differentiate these different conditions we believe that in some particular cases, a short course of combined corticoid-antibiotics treatment with sinus X ray before and after treatment, may be useful. In case of confirmed sinusitis (sinus visualization after treatment), a secondary preventive treatment may reduce the risk of chronic maxillary sinusitis. We suggest that further studies should be performed in order to better define the reality of chronic ethmoido-maxillary sinusitis in infants younger than 18 months of age, and to study the possible role of a phenomenon of immuno-inflammatory trapping in its pathologenesis.