Background Poor oral health (OH) is a risk factor for systemic disease and lower quality of life (QoL). Patients with inflammatory dermatologic/rheumatologic diseases report more oral discomfort, dry mouth, and periodontal disease than controls. Medications used to treat these conditions can also adversely affect OH. Objectives The aim was to assess the OH of patients with chronic inflammatory dermatologic/rheumatologic diseases treated with systemic/biologic therapy, compared to controls. Methods Patients with chronic inflammatory dermatologic/rheumatologic diseases treated with systemic/biologic therapy were recruited from outpatient clinics across two university hospitals. All patients had a standardized World Health Organisation OH assessment performed consisting of an OH exam and questionnaire. Age‐ and sex‐matched controls without chronic inflammatory disease were recruited from a pigmented lesion clinic. Charts of patients with chronic inflammatory dermatologic/rheumatologic diseases were reviewed to assess OH documentation. Results One hundred patients were examined (50 cases and 50 controls). Patients with inflammatory dermatologic/rheumatologic diseases (cases) had poorer periodontal status (mean loss of attachment 6.9 mm vs. 1.9 mm controls, p = 0.01), more missing teeth (mean 7.7 vs. 4.4 controls, p = 0.029), more dry mouth (82% vs. 20% controls, p = 0.001), and less frequent tooth brushing (60% vs. 80% controls, p = 0.037). Of 250 patient charts which were reviewed, 98.4% (n = 246) had no documentation of OH. Conclusion Patients with severe inflammatory dermatologic/rheumatologic conditions have poorer OH and OH‐related QoL. Clinicians should appreciate the risk of poor OH in this cohort and have a low threshold for involving OH professionals in care pathways for severe inflammatory disease.