BACKGROUND: Limited data exist on the burden of comorbidity among patients with squamous cell head and neck cancer (SCCHN) before and during cancer treatment. METHODS: The precancer prevalence and incidence rates of 8 comorbid conditions were estimted among a population-based cohort of 1499 patients with SCCHN in the Netherlands. Patients with cancer, treatments, and comorbidities were identified in the PHARMO Record Linkage System (RLS) using hospital admissions and/or dispensing codes. Prevalence proportions and incidence rates were also compared against a matched cancer-free population. RESULTS: Cardiovascular (41%) and respiratory diseases (12%) were the most prevalent comorbidities. Incidence rates of most comorbidities were highest the first 6 months after cancer diagnosis and decreased over time. Patients receiving chemotherapy-based treatment had significantly higher incidence rates of anemia and other malignant diseases. CONCLUSIONS: High rates of acute and chronic comorbidity were observed; knowledge of comorbidity burden aids in establishing a benefit-risk profile for investigational SCCHN therapies.