Oligonucleotides (ONs) are short fragments of nucleic acids, currently being investigated as therapeutic agents. When administered subcutaneously (sc), ONs cause a specific local reaction originating around the injection site, such as erythema, itching, discomfort and pain, including more severe manifestations such as ulceration or necrosis. These injection site reactions (ISRs) are common, but rather poorly described in the literature. With this review, we aim to provide an overview on the extent of the problem of ISRs, based on reported incidence. A structured literature search was performed to identify reported incidence and clinical features of ISRs which yielded 70 manuscripts that contained information regarding ISRs. The data from literature was combined with data on file available at our institution. All sc administered ONs described in the literature lead to the occurrence of ISRs. The percentage of trial subjects that developed ISRs ranged from 22 to 100% depending on ON. The majority of ONs caused ISRs in more than 70% of the trial subjects. The severity of the observed reactions varied between different ONs. Occurrence rate as well as severity of ISRs increases with higher doses. For chemistry and target of the compounds, no clear association regarding ISR incidence or severity was identified. All ONs developed to date are associated with ISRs. Overcoming the problem of ISRs might add greatly to the potential success of sc-administered ONs. Knowledge of these skin reactions and their specific immunostimulatory properties should be increased in order to obtain ONs that are more suitable for long-term use and clinically applicable in a broader patient population. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Oligonucleotides are promising drug candidates that are being thoroughly investigated for therapeutic effects for various indications.• To date, only very few data are available on injection site reactions after subcutaneous oligonucleotide administration. WHAT THIS STUDY ADDS• A structured literature search of injection site reactions combined with data on file available at the Centre for Human DrugResearch reveal clearly the clinical importance of understanding this within-class adverse effect.