Consecutive Hemophilus influenzae type b (Hib) isolates (333 total) from children with invasive disease in Finland in 1985-1986 were analyzed. All belonged to the common genetic clusters described in the USA and Europe. However, detailed typing demonstrated some characteristics unique to Hib strains in Finland. Of the isolates, 86% belonged to one of four distinct patterns according to the combination of outer membrane protein subtype, biotype, and lipopolysaccharide serotype: 1-I-1 (25%), 1-II-9 (8%), and 1c-I-1 (18%). Pattern 1-II-9 has not been previously reported; it was most commonly found in the most densely populated area of Finland and among children cared for outside the home. Multilocus enzyme electrophoresis revealed that 87% of isolates with the pattern 1c-I-1 belonged to the electrophoretic type 21.8, which is seldom recovered from patients with invasive Hib disease in other countries.