Colonization of airways with Pseudomonas aeruginosa (PA) is known to be a risk factor for infection and adverse clinical outcome in patients with cystic fibrosis (CF). Whereas infections with PA have been linked to contaminated medical devices in hospitals, sources of colonization and infection with PA in households of patients with CF remain to be identified. Using a standardized sampling protocol, we prospectively examined the presence of PA in 102 households of patients with CF in Germany. PA was detected in 73 (71.6%) of 102 households. PA was detected most frequently in drains of showers (39.6%), drainpipes of hand-basins in kitchens (35.0%) and bathrooms (34.7%), and drainpipes of toilets (26.5%). Toilet seats and dish-clothes did not show PA in any household. The frequency and intensity of cleaning measures did not impact the detection rate of PA. Results of the present study for the first time determinate the rate of contamination with PA in households of patients with CF. Future studies will determine the risk of transmission of PA from households locations to patients with CF.