Acute and long-term changes in serum lipids after acute stroke. We studied serum lipid profiles in 171 patients less than or equal to 48 hours after the onset of acute stroke and 3 months later. The 83 patients suffering cerebral infarction had significantly higher serum concentrations of total cholesterol, low density lipoprotein-cholesterol, and apolipoprotein B and significantly lower serum concentrations of triglycerides and lipoprotein (a) less than or equal to 48 hours after ictus than 3 months later. The lipid profiles of the 53 patients suffering lacunar infarction were similar on both occasions, the only significant differences being higher total cholesterol and low density lipoprotein-cholesterol concentrations less than or equal to 48 hours after ictus. No significant changes were observed among the 35 patients suffering cerebral hemorrhage apart from a significantly higher concentration of high density lipoprotein3-cholesterol less than or equal to 48 hours after ictus. Our study, with many patients classified according to stroke subtype, gives results different from those of previous studies with much fewer patients. We conclude that in studies of serum lipid and lipoprotein concentrations as risk factors for cerebral infarction, comparing values obtained less than or equal to 48 hours after admission with control values may incorrectly identify certain lipid fractions as risk factors. 