At present, no definite conclusions can be drawn about the real extent of the pain suffered by cancer patients. A population-based study was conducted to obtain reliable information about the prevalence and severity of pain in cancer patients (all phases) and about predictors of pain. A representative sample of cancer patients was recruited in the area from a cancer registry. Pain was assessed by the Brief Pain Inventory (BPI). Adequacy of pain treatment was assessed with the Pain Management Index (PMI). We found that 55% of the 1429 respondents had experienced pain past week; in 44% (n=351), the pain was moderate to severe (BPI score>or= 4). Total prevalence of pain/moderate to severe pain was present in 49%/41% in patients with curative treatment >or=6 months ago, 57%/43% in patients with current curative treatment or treatment <6 months ago, 56%/43% in patients with current palliative anti-cancer treatment and in 75%/70% in patients for whom treatment was no longer feasible. Positive predictors of the prevalence of pain were lower education level, more advanced disease and haematological (excluding (non)-Hodgkin lymphoma), gastro-intestinal, lung, or breast malignancies. According to the PMI, analgesic treatment was inadequate in 42% of the patients. Negative predictors of adequate treatment were current curative anti-cancer treatment and low education level. CONCLUSION: A substantial proportion of cancer patients does suffer from moderate to severe pain and does not receive adequate pain treatment.