The effects of oxidised LDL (oxLDL) on cell proliferation, apoptosis and hormone-induced differentiation have been evaluated for the first time in 3T3-L1 preadipocytes. Unlike control cells, oxLDL-treated preadipocytes showed a high proliferation rate, a low apoptosis level, and an impaired differentiation process with an increased preadipocyte factor-1 (Pref-1) mRNA expression at late times. By silencing Pref-1 mRNA or inhibiting its expression with an increased dexamethasone concentration, differentiation occurred as usual, which demonstrates the key role of Pref-1 overexpression. The results suggest a specific action of oxLDL on the adipogenesis inhibitor Pref-1, as indicated also by its reappearance in mature adipocytes treated with oxLDL. The inhibitory effects of oxLDL on differentiation required oxLDL uptake by CD36, and were associated with lipoprotein lipids. These results point to oxLDL as a modulator of adipose tissue mass and as possible link between obesity and its clinical complications.