We have presented three patients representing three of the four reported forms of C1 esterase inhibitor deficiency. The C1INH deficiencies are in general distinguishable from each other and from other forms of angioedema by their complement patterns. The acquired C1INH deficiency must be part of the differential in patients without a family history of angioedema since it may precede the diagnosis of more serious medical conditions such as lymphoproliferative disorders.