Diagnosing a patient who presents with abdominal pain and altered bowel habits can be challenging. Although serious organic illnesses can cause these symptoms, irritable bowel syndrome is commonly responsible. It can be difficult to properly evaluate these patients without overusing diagnostic tests and consultation. A practical approach for diagnosing irritable bowel syndrome is suggested, using the Rome II criteria and the presence of alarm symptoms such as weight loss, gastrointestinal bleeding, anemia, fever, or frequent nocturnal symptoms as starting points. If there are no alarm symptoms and the Rome II criteria are not met, it is acceptable to reevaluate the patient at a later date. If there are no alarm symptoms and the Rome II criteria are met, the patient should be categorized on the basis of age: patients 50 years or younger can be evaluated on the basis of predominant symptoms--constipation, diarrhea, or abdominal pain. Patients older than 50 years should be fully evaluated and considered for gastroenterology referral. If alarm symptoms are present, a full evaluation should be performed (and gastroenterology referral considered), regardless of the patient's age.