A deep knowledge of the anatomy, physiology and pathology of the species that are been investigated is mandatory for the correct interpretation of diagnostic imaging. Radiology is the first resource used in herpetological medicine. Skeletal fractures are not rare in reptiles kept in captivity. They are usually assessed by means of plain radiographs. The clinician should be aware that in reptiles the fracture healing process involves a mixture of fibrous tissue and osseous callus; therefore, the clinical fracture stability occurs far before radiographic healing becomes evident. Metabolic bone diseases are also extremely common but the radiographic visualization of the bone loss is only possible when the loss of density is over 40%. Other than skeletal disorders radiology can rapidly identify gastrointestinal disorders (dilation, foreign body obstruction), coelomic conditions, neoplasia or reproductive problems. Especially in chelonians and lizards, follicular stasis or dystocia can be diagnosed via this imaging technique. In lizards (such as iguanas or chameleons), another frequently encountered condition is renal disease. The enlargement of the kidneys can be seen as a direct sign on the lateral view. Secondary signs of kidney disease can be dilation of the intestinal tract, secondary to the enlargement of the kidneys that can impede the passage of feces through the pelvic canal. The kidneys lie in the pelvic area and can be visualized via a dorsal approach just cranial to the iliatic bones. In chelonians horizontal radiographic beam orientation and horizontal positioning (lateral and cranio-caudal) are often necessary to reduce errors in radiographic interpretation of the lung, bladder and internal organs. Although radiology is still very often use as the most common imaging technique in reptiles, ultrasonography and CT scanning are gaining ground, due to the fact that they can be used to evaluate any systems in a reptile: the heart, liver, gallbladder, urinary bladder intestine and reproductive tract. Reptiles with thick and calcified scales can be problematic for ultrasonography due to artifacts caused by air pockets between the scales. Giving the patient a warm bath prior to investigation will reduce the potential air pockets, as will spraying the patient with water prior to applying the ultrasound gel. Animals undergoing ecdysis can also be problematic to scan due to the air between the old and the new skin layers. In small patient a water bath can be used with the transducer submerged below the surface. Lizards can be placed in dorsal recumbency with the probe directed downwards or held in ventral recumbency with the probe directed from below. The ventral body wall is the main approach and provides information on the majority of the coelomic organs. In young chelonians or soft-shelled subjects, scanning trough the shell is possible and this can be directed over the area of interest. In adult chelonians the sites available for ultrasound are the prefemoral fossa and the region between the neck and the thoracic inlet.