Objectives The International Agency for Research on Cancer controversially has classified formaldehyde as a cause of nasopharyngeal carcinoma and myeloid leukaemia. To provide further information on the risks of cancer from formaldehyde, we extended follow-up of 14 008 male chemical workers at six factories in England and Wales.

Method The cohort was identified from employment records, and exposures to formaldehyde were classified on the basis of job title. Subjects were traced through health service records, and their mortality was compared with national death rates by the person-years method. Associations of exposure with incident upper airways cancer and leukaemia were further explored in nested case-control analyses.

Results More than 2000 additional deaths had occurred since last follow-up of the cohort. Excess deaths were observed from cancers of the oesophagus (100 v 93.2 expected), stomach (182 v 141.1), rectum (107 v 86.8), liver (35 v 26.9) and lung (813 v 645.6), but none of these tumours exhibited a clear exposure-response relationship. In nested case-control analyses of 115 men with upper airways cancer (including one nasopharyngeal cancer), 92 with leukaemia, and 45 with myeloid leukaemia, there were no elevations of risk in the highest exposure category (>2 ppm for ≥1 year). When the two highest exposure categories were combined, the odds ratio for myeloid leukaemia was 1.26 (95% CI 0.39–4.08).

Conclusions Our results provide no support for a hazard of myeloid leukaemia, nasopharyngeal carcinoma or other upper airways cancer from formaldehyde, and indicate that any excess risk of these diseases, even from relatively high exposures, is at most small.