Mutational defects in the LDL receptor are responsible for familial hypercholesterolemia (FH); thus far more than 150 mutations have been described. Nevertheless, systematic searches among the Germans have not been conducted. We used single-strand conformational polymorphism and polymerase chain reaction to find mutations in 10 index patients and in 40 other individuals with heterozygous FH. Our screen in the 10 index patients revealed 7 hitherto undescribed mutations. A screen of the 40 additional FH patients disclosed 20 defective of 54 total alleles and allowed specific diagnoses in 88 family members. We also found two families in which the children were markedly affected by FH, but the expected parental expression of the trait was not manifest. This observation suggests a role for additional environmental and genetic influences. Our report represents the first comprehensive effort to identify FH mutations in Germany. We found 10 mutations and these mutations explain 37% of FH cases. Our data may have relevance to expected FH patterns in central Europe.