Abstract For the posterior interosseus nerve syndrome (PINS), no randomised controlled trials or controlled clinical trials about the effectiveness of interventions are available; only case series can be found. Although the validity of case series is inferior to controlled trials, they may provide valuable data about the efficacy of treatment options. Therefore, we systematically reviewed all available observational studies on treatment of PINS. A literature search and additional reference checking was done. On the basis of previous checklists, we constructed a quality assessment and rating system to analyse the included case series. Studies with less than 50% of the maximum points on the methodological quality assessment were excluded from the analysis. The results are summarised according to a rating system for the strength of the scientific evidence. Six eligible case series for this review were found. After the data extraction and methodological quality assessment, two higher quality studies that evaluated the effectiveness of surgical decompression of the PIN were included in the final analysis. There is a tendency for the effectiveness of surgical decompression of the PIN in patients with PINS. The effectiveness of a conservative treatment for PINS is unknown because no higher quality studies are available. Additional high-quality controlled studies are needed to assess the level of ‘conclusive evidence’ for surgical treatment. There is also a need for high-quality controlled trials into the effectiveness of conservative treatments for PINS.