A study on blood clotting has been carried out in a number of obese individuals and compared to a group of non-obese persons, in order to assess if the former can be considered to be in "high risk" regarding the onset of a thromboembolic process. The technique of thromboelastography was chosen. The results point out that in obese people a series of alterations take place, both in the time of clot formation, which is enlarged, as in the organization of its nets, which appear strongly structured, favoured by the hyperfibrinogenemia and thrombocytosis detected in these subjects. Likewise, the effect of a hypocaloric diet on clotting in obese persons has been evaluated and compared with the former groups. Clotting in treated obese individuals is modified in the same way as in the untreated group when compared to the non-obese population; nevertheless, when both groups of obese people are compared, no significant difference is observed in the different parameters studied, even though constants determined in citrated whole blood are closer to normality in the subjects undergoing caloric restriction.