The role of sanitation in performance of insecticidal bait stations containing 0.5% chlorpyrifos against the American cockroach, Periplaneta americana (L.), was investigated in residential premises. Test sites were chosen from three locations in Penang Island, Malaysia, and clustered according to their sanitary conditions. Results indicated that at 1-week post-treatment, houses with good sanitary conditions showed a significantly faster reduction (P > 0.05) in the number of cockroaches trapped (> 95%) than those with moderate and poor conditions. At 6 weeks post-treatment, all houses treated with insecticidal baits showed no significant difference in terms of reduction rate of cockroach numbers (P > 0.05), irrespective of sanitary condition. However, the bait performance in houses with poor sanitary conditions could not be sustained up to 12-week post-treatment.