Microplastics are ubiquitous in ecosystems and a lot of research is being performed to understand their environmental fate and effects on organisms. However, the release and impact of MP has so far not been considered in LCA studies. This is due to missing information on the inventory side about microplastic releases and missing Characterization Factors to quantify the effects of MP. The goal of this study was to elucidate the relevance of MP release into freshwaters from an LCA perspective, by using worst-case assumptions. In accordance with the USEtox framework, an interim and simplified Characterization Factor for the impact category of freshwater ecotoxicity was calculated to be 3231 PAF·m3·d·kg−1. Applying this Characterization Factor, two LCA case studies were conducted, one on a polyester T-Shirt and one with a shower gel containing microplastics. The results show a small contribution of microplastics to the freshwater ecotoxicity for a scenario with state-of-the-art wastewater treatment. Different scenarios varying in microplastic release and removal during wastewater treatment and a sensitivity analysis of the Characterization Factor allowed identifying the potential range of the microplastic contribution to the overall ecotoxicity. In conclusion, the inclusion of microplastic release into LCA only marginally influences the overall environmental effects of the two products in the LCA case studies.