Background: Foot intertrigo is mostly caused by dermatophytes and yeasts, less frequently by gram-positive and gram-negative bacteria. Nevertheless, the importance of polymicrobial infections and especially colonizations of Pseudomonas aeruginosa can cause therapy problems in relation to antibiotic resistance and the risk of potentially lethal complications. Objective: The aim of this study was to evaluate the main epidemiologic and clinical features of intertrigo from gram-negative bacteria, the function of promoting factors, and the measures taken to treat and prevent this disorder. Methods: Between 1989 and 1998, 123 cases of intertrigo from gram-negative bacteria were observed at the Cagliari University Dermatology Department. Routine clinical and blood examinations, repeated bacterioscopic and mycologic examinations, cultures aimed at identifying the responsible bacteria, and antibiograms were performed. Results: P aeruginosa was found to be the prevailing pathogen, both alone and associated with other gram-negative bacteria (such as Escherichia coli, Proteus mirabilis, Morganella morganii) and gram-positive bacteria. Clinical manifestations were similar in the majority of patients: erythema, vesicopustules, erosions, and marked maceration caused by abundant, malodorous exudate. Lesions affected the interdigital spaces of both feet and frequently extended to the planta and the back of the toes. Patients complained of burning and pain. Successful therapies were achieved with combined topical and systemic treatment; to avoid the risk of antimicrobial resistance, the choice of the active antibiotic was guided by antibiograms. Conclusion: In all symptomatic toe web infections, the presence of gram-negative germs, such as P aeruginosa, should be investigated to avoid the risk of treatment failures and more severe local or systemic complications. (J Am Acad Dermatol 2001;45:537-41.)