In a survey of 162 keratoconus patients, the relationship of individual conditions, such as asthma, hay fever, connective tissue syndromes and eye rubbing, to keratoconus was investigated. The prevalence of asthma rose from 0.4% to 1% in the control group to 17.9% in the keratoconus group, or an 18-fold increase. The incidence of hay fever in keratoconus patients was 35.7%. As multifactorial disorders, keratoconus and asthma may share some of the multiple genes necessary for the expression of the disorder. Previous findings of excessive eye rubbing in keratoconous patients were confirmed by this study. The incidence of connective tissue disorders associated with keratoconus was negligible.