In a 30 year follow up study of 8526 men aged 20 and over in the Rhondda Fach 99.9% of the population was traced. Generally, the results are similar to those found in a 20 year follow up of the same subjects. Miners and ex-miners had an excess mortality compared with non-miners, but within the former only those who had had categories B and C pneumoconiosis showed a raised mortality. Category A pneumoconiosis was not associated with any excess compared with other miners and ex-miners. Two further aspects of the data relating to gastric cancer and progressive massive fibrosis will be examined in later reports.