Background: Small-sided soccer games (SSSG) are a specific exercise regime with two small teams playing against each other on a relatively small pitch. There is evidence from original research that SSSG exposure provides performance and health benefits for untrained adults. Objectives: The aim of this systematic review was to summarize recent evidence on the acute and long-term effects of SSSG on physical fitness, physiological responses, and health indices in healthy untrained individuals and clinical populations. Materials and Methods: This systematic literature search was conducted in four electronic databases (PubMed, Web of Science, SPORTDiscus) from inception until June 2019. The following key terms (and synonyms searched for by the MeSH database) were included and combined using the operators "AND", "OR", "NOT": ((soccer OR football) AND ("soccer training" OR "football training" OR "soccer game*" OR "small-sided soccer game*") AND ("physical fitness" OR "physiological adaptation*" OR "physiological response*" OR health OR "body weight" OR "body mass" OR "body fat" OR "bone composition" OR "blood pressure")). The search syntax initially identified 1,145 records. After screening for titles, abstracts, and full-texts, 41 studies remained that examined the acute (7 studies) and long-term effects (34 studies) of SSSG-based training on physical fitness, physiological responses, and selected health indices in healthy untrained individuals and clinical populations. Results: No training-related injuries were reported in the 41 acute and long-term SSSG studies. Typically, a single session of SSSG lasted 12 to 20 minutes (e.g. 3x4 min with 3 min rest or 5x4 min with 4 min rest) involving 4 to 12 players (2 vs. 2 to 6 vs. 6) at an intensity ≥80% of HR max. Following single SSSG sessions, high cardiovascular and metabolic demands were observed. Specifically, based on the outcomes, the 7 acute studies reported average heart rates (HR) ≥80% of HR max (165-175 bpm) and mean blood lactate concentrations exceeding 5 mmol/l (4.5-5.9 mmol/l) after single SSSG sessions.