Lipoprotein (a) [Lp(a)] is a low density lipoprotein (LDL) with one apolipoprotein (a) molecule bound to the apolipoprotein B-100 of LDL. Lp(a) is an independent risk factor for cardiovascular disease (CVD). However, the relationship of Lp(a) to diabetes and metabolic syndrome, both known for increased CVD risk, is controversial. In a population based study on type two diabetes mellitus (T2DM) development in women, Lp(a) plasma levels showed the well known skewed distribution without any relation to diabetes or impaired glucose tolerance. A modified clot lysis assay on a subset of 274 subjects showed significantly increased clot lysis times in T2DM subjects, despite inhibition of PAI-1 and TAFI. Lp(a) plasma levels significantly increased the maximal peak height of the clot lysis curve, indicating a change in clot structure. In this study Lp(a) is not related to the development of T2DM but may affect clot structure ex vivo without a prolongation of the clot lysis time.