Patients admitted during a 6-month period to a maternity hospital in Saudi Arabia were studied for nosocomial infections and misuse of antibiotics. Patient history and diagnosis on admission and subsequent clinical and laboratory data were analysed. Infection developing from 72 h after admission was considered nosocomial. Therapeutic and prophylactic data as recorded on the patients' charts were assessed for possible misuse of antibiotics. Of 3439 patients, 136 (4.0%) developed nosocomial infection: 2.0%, 8.9% and 37.7% in obstetric, gynaecologic and nursery patients, respectively. Infections among adults were mostly found in the urinary (44.4%) and lower genital (33.3%) tracts. Among newborns, over 70% of cases were eye and ear (29.8%), skin (26.2%) and blood (19.0%) infections. Gram-negative bacteria caused 65.7% of the infections. Over 90% of the bacterial isolates were multidrug-resistant. About 24% of patients received single or multiple antibiotics; 57.2% were misused. The minimal hospital cost estimate for both nosocomial infections and misused antibiotics was US $318,705. The findings of this study, the first of its type in this region, should prompt improved infection control measures as well as educational and antibiotic restriction interventions.