Many different portable monitors have been used to assess patients with suspected sleep apnea. There is limited evidence for the use of type 2 monitors, especially in the unattended setting in which there may be high rates of data loss. Type 3 monitors have low likelihood ratios for negative tests and can be used to "rule out" sleep apnea. The ability of type 3 monitors to "rule in" sleep apnea is less convincing, but this may improve with the use of improved technology, such as nasal pressure transducers. Type 4 monitors usually use oximetry and can be used to "rule out" sleep apnea. Higher sampling rates and improved analysis algorithms can improve the specificity of these monitors; hence, likelihood ratios for a positive test result can be high enough with some monitors to "rule in" sleep apnea as well. Not all monitors record and analyze signals in the same way; it is not possible to generalize results from one monitor across all monitors of a particular type. Limited evidence is available for many portable monitors in the unattended setting, and further research is required in this area. Clinicians should identify how they plan to use a portable monitor: as a mechanism to exclude disease in asymptomatic snorers, to confirm disease in [figure: see text] patients with a high clinical probability of disease, or to risk stratify patients so that proper priority for polysomnography can be determined. This determination allows them to select a portable monitor with signals most appropriate to their needs. The quality of the validation studies for each portable monitor also should be evaluated carefully before implementation in clinical practice. The ability for a clinician to review raw data manually and consider artifact is a necessary feature. Measurement of oxygen saturation also is important to identify patients with previously unsuspected serious desaturation that would indicate the need for more urgent treatment. In centers in which polysomnography is not readily available, a clinical decision algorithm that incorporates a clinical prediction rule with the use of portable monitors can guide clinicians toward institution of therapy or further investigations. Intuitively, this approach could reduce waiting times for polysomnography and delays in diagnosis, but additional evidence for the validity and cost effectiveness of this approach is required.