The authors conducted a mailed questionnaire survey of a 5% sample of the cohort of 20643 people officially recognized by the Spanish government as having had toxic oil syndrome, a previously undescribed illness that was epidemic in Spain in 1981.

After three mailings of a letter and questionnaire, responses for only 66% of the sample had been received.

Nevertheless, responses were obtained from virtually all remaining patients (or surrogates for them in the cases of patients that had died) when they were sought by telephone.

In 1981, there was clear-cut excess mortality in the cohort (standardized mortality ratio [SMR] 6.51; 95% confidence interval [Cl]:3.92-10.17).