The contribution of dietary trans fatty acids (TFAs) on the risk of ischemic heart disease (IHD) has recently gained further support due to the results from large, prospective, population-based studies. Compared to saturated fat, TFAs are, gram to gram, associated with a considerably (2.5- to >10-fold) higher risk increment for IHD. A negative effect on the human fetus and on newborns and an increase in colon cancer risk in adults are possible but, however, still equivocal. Recent findings justify further studies concerning the effect of TFAs on allergic diseases in children and on the risk of type-2 diabetes in adults. The intake of industrially produced TFAs in European countries is decreasing. However, determination of the TFA content in various popular food items collected in Danish shops showed that it is likely that persons with a frequent intake of, e.g., French fries, microwave oven popcorn, chocolate bars, fast food, etc., consume industrially produced TFAs in amounts far exceeding the average intake, and are thereby exposed to an unnecessary health risk. The Danish government has decided that oils and fats containing more than 2% industrially produced TFAs will not be sold in Denmark after the January 1, 2004.