Objective Bacterial infection is a common finding in acute sialadenitis and may play a role in the chronicity of the condition. This study investigated if bacterial biofilm is present in submandibular chronic obstructive sialadenitis.Methods A descriptive case-control study was conducted that compared 10 histological sections of submandibular glands with chronic obstructive sialadenitis, to 10 histological sections of the healthy part of submandibular glands with pleomorphic adenoma. Fluorescence in situ hybridisation and confocal laser scanning microscopy visualised evidence of bacterial biofilm.Results In the chronic obstructive sialadenitis group, 5 out of 10 histological sections showed morphological evidence of bacterial biofilm. In the control group, there was no sign of bacterial biofilm formation.Conclusion Morphological evidence of bacterial biofilm was found in the submandibular gland sections from patients with chronic sialadenitis and suggests a role in the chronicity of submandibular chronic obstructive sialadenitis.