OBJECTIVES: Smartphones incorporate multiple inbuilt sensors to enhance user experience and provide certain features. More recently, novel application of these inbuilt sensors has enabled new and inventive uses for the smartphone in clinical research. We reviewed published validation studies performed that compare clinical outcomes assessments derived from smartphone sensor data to gold standard approaches. METHODS: We categorized studies in our review into the areas of application and summarized validation findings. We eliminated studies validating PRO instruments and those using external sensors or adapters connected to smartphones. RESULTS: Eight validation studies reported use of the smartphone accelerometer and gyroscope to measure joint angles and range of motion including shoulder, knee and spine, compared to goniometer, scoliometer and other approaches. Correlations varied between methods and outcomes measured: range of motion (ROM), flexion angles (r>0.99), cervical rotation (ICC< 0.55). Balance and gait were assessed in five studies in comparison to research-grade accelerometers: showing moderate to strong correlations (r=0.76 to 1.00) in displacement and time measures; two studies showed good correlation for some parameters measured in the Timed Up and Go test, and one in assessment of bradykinesia in Parkinson’s (PD) patients. One study showed good to strong correlation of tremor parameter measures via smartphone compared to ClinRO data (r>0.70). Two studies showed high correlation between heart rate measured when the index finger is pressed against the rear camera and illuminated by the phone’s light-emitting diode in comparison to a pulse oximeter (ICC>0.93, r=0.99). CONCLUSIONS: Smartphone inbuilt sensors and components may offer a convenient and low cost approach to measurement of performance outcomes. Variability between approaches is inherent due to methodology and algorithm differences. Some approaches provide positive indications in comparison to gold standard methodologies, but more research in larger studies is encouraged for wider scale utility.