The immune checkpoint inhibitors pembrolizumab and nivolumab together with their diagnostic assays have recently been granted market authorization for treatment of advanced non-small-cell lung cancer in the USA. The two assays, PD-L1 IHC 22C3 pharmDx and PD-L1 IHC 28-8 pharmDx (both by Dako, Glostrup, Denmark), are the first PD-L1 IHC assays to obtain regulatory approval through the Premarket Approval process. This approval is supported by recent clinical studies that have shown a positive correlation between PD-L1 expression and the outcome following treatment with different PD-1/PD-L1 checkpoint inhibitors. These diagnostic assays are able to identify the group of non-small-cell lung cancer patients who will benefit most from treatment with the immune checkpoint inhibitors. However, so far, it is only the PD-L1 IHC 22C3 pharmDx assay, which is linked to the use of pembrolizumab, that has obtained regulatory status as a companion diagnostic.