Eight of 600 Holstein heifers and cows died after ingestion of sweet clover silage (Melilotus sp) that contained excessive concentrations of dicumarol caused by mold infestation. The cattle developed subcutaneous hemorrhages and bled from the vagina, became weak, were unable to move, and died. To the best of our knowledge, this is the first report of sweet clover poisoning in cattle from California and is discussed in light of previous findings in the Midwest and Canada. Sweet clover poisoning is caused by dicumarol, a fungal metabolite produced from substrates in sweet clover, and is a common livestock problem in the Northern Plains and Canada. Sweet clover poisoning should be considered in livestock animals with clinical evidence of hemostatic dysfunction, prolonged coagulation times, subcutaneous hemorrhages, and hemorrhagic abortions. Definite diagnosis of moldy sweet clover poisoning can be accomplished by analysis of serum and feed samples for dicumarol concentrations.