Cockroach (CR) infestation is an important cause of sensitization in allergic individuals. We investigated the prevalence and the characteristics of sensitivity to CRs in patients with respiratory allergy in Izmir. Three hundred and fifty-four patients with allergic rhinitis and/or asthma responded to a questionnaire and were prick tested with CR extract as well as with extracts of other household allergens. One hundred and twenty-eight of these patients (36.2%) were sensitized to CRs-, sensitivity was 1.4 times more frequent among men compared to women. The prevalence of asthma was 39.1% in the group of individuals sensitized to CRs and 28.8% in the non-sensitized group (95% confidence intervals (CI) 1.005-2.508; P = 0.047). Moderate, persistent asthma was reported more often in patients sensitized compared to patients not sensitized to CRs (30% versus 18%). In patients with allergic rhinitis, the mean time before they became asthmatic was less in the group sensitized compared to those not sensitized to CRs (2.8 +/- 3.4 versus 4.5 +/- 5.2 years, P = 0.045). More than half the patients sensitized CRs were also sensitized to cats (68.9%), to dog dander (62.1%) and to Dermatophagoides pteronyssinus (59.8%). We conclude that allergy to CRs is present in a large number of atopic individuals in Izmir. The existence of allergy to CRs seems to shorten the delay in the onset of asthma in patients with allergic rhinitis. (C) 2004 Elsevier SAS. All rights reserved.