Past research has failed to adequately address the reasons behind the lack of handwashing in public restrooms. The present study explores possibilities for using psychology to design effective handwashing interventions. Specifically, the current study examines whether (1) the frequency of reported handwashing differs from that of actual handwashing behavior and (2) the presence of a sign increases handwashing behavior. Participants self-reported their handwashing behavior and/or their handwashing was observed in a public restroom. In the observation portion of the study, the experimenters either observed participants’ natural behavior or posted a sign in the restroom that read “Washing your hands after going to the bathroom reduces your risk of catching or spreading infectious diseases such as salmonella or hepatitis A” before observing their handwashing behavior. The experimenters recorded whether participants washed their hands with water and soap, with water but no soap, or not at all. Participants reported significantly higher rates of handwashing than were observed. Additionally, the reported and observed handwashing behavior of women exceeded that of men. Finally, men used soap more when presented with the sign than when no sign was present. In all, this study suggests that many serious diseases and illnesses can be avoided by increasing handwashing by posting signs in public restrooms reminding people to wash their hands.