The aim of this PRISMA-compliant systematic review was to analyze the evidence pertaining to disease resolution after the treatment of peri-implant diseases with the following PICO question: What is the rate of disease resolution following nonsurgical and surgical therapy for peri-implant diseases in adult human subjects? A literature search to identify studies that fulfilled preestablished eligibility criteria was conducted. Data on primary therapeutic outcomes, including treatment success and rate of disease resolution and/or recurrence, as well as a variety of secondary outcomes were extracted and categorized. A total of 54 articles were included. Few studies investigated the efficacy of different nonsurgical and surgical therapies to treat peri-implant diseases using a set of predefined criteria and with follow-up periods of at least 1 year. The definition of treatment success and disease resolution outcomes differed considerably among the included studies. Peri-implant mucositis treatment was most commonly reported to be successful in arresting disease progression for ≤ 60% of the cases, whereas most studies on peri-implantitis treatment reported disease resolution occurring in < 50% of the implants. Disease resolution is generally unpredictable and infrequently achieved after the treatment of peri-implant diseases. A great variety of definitions have been used to define treatment success. Notably, percentages of treatment success and disease resolution were generally underreported. The use of standardized parameters to evaluate disease resolution should be considered an integral component in future clinical studies.