Consumer health technologies can educate patients about diabetes and support their self-management, yet usability evidence is rarely published even though it determines patient engagement, optimal benefit of any intervention, and an understanding of generalizability. Therefore, we conducted a narrative review of peer-reviewed articles published from 2009 to 2013 that tested the usability of a web- or mobile-delivered system/application designed to educate and support patients with diabetes. Overall, the 23 papers included in our review used mixed (n = 11), descriptive quantitative (n = 9), and qualitative methods (n = 3) to assess usability, such as documenting which features performed as intended and how patients rated their experiences. More sophisticated usability evaluations combined several complementary approaches to elucidate more aspects of functionality. Future work pertaining to the design and evaluation of technology-delivered diabetes education/support interventions should aim to standardize the usability testing processes and publish usability findings to inform interpretation of why an intervention succeeded or failed and for whom.