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There has been a substantial increase in the use of computed tomography (CT) and magnetic resonance imaging (MRI) in pregnancy and lactation. Among some physicians and patients, however, there are misperceptions regarding risks, safety, and appropriate use of these modalities in pregnancy. We have developed a set of evidence-based guidelines for the use of CT, MRI, and contrast media during pregnancy for selected indications including suspected acute appendicitis, pulmonary embolism, renal colic, trauma, and cephalopelvic disproportion. Ultrasonography is the initial modality of choice for suspected appendicitis, but if the ultrasound examination is negative, MRI or CT can be obtained. Computed tomography should be the initial diagnostic imaging modality for suspected pulmonary embolism. Ultrasonography should be the initial study of choice for suspected renal colic. Ultrasonography can be the initial imaging evaluation for trauma, but CT should be performed if serious injury is suspected. Pelvimetry now is used rarely for suspected cephalopelvic disproportion, but when required, low-dose CT pelvimetry can be performed with minimal risk. Although iodinated contrast seems safe to use in pregnancy, intravenous gadolinium is contraindicated and should be used only when absolutely essential. It seems to be safe to continue breast-feeding immediately after receiving iodinated contrast or gadolinium. Although teratogenesis is not a major concern after exposure to prenatal diagnostic radiation, carcinogenesis is a potential risk. When used appropriately, CT and MRI can be valuable tools in imaging pregnant and lactating women; risks and benefits always should be considered and discussed with patients.