The work environment of an iron foundry involved a large number of exposures related to several health problems, mainly lung cancer. "Altos Hornos del Mediterráneo (AHM)" fron Sagunto is an iron industry that stopped its foundry plant production in 1984. The present paper shows the methodological problems merged during the reconstruction of AHM workers' cohort. From personnel files a male cohort was defined for 7,018 males who worked at least one year and started work between 1950 and 1970, following them through 1991. The cause of death was obtained from de Civil register, Life insurance and reference hospitals. By means of experts the work areas were rated in three exposure levels. 6% of cohort members were lost during the follow-up. 2786 deaths were reported and 88% causes of death were retrieved. The enterprise data files let us to reconstruct the cohort, but the availability of a National Death Index, as there is in other countries would have made easier the job and would have improved the data quality.