Data on ingestion of microplastics by marine biota are quintessential for monitoring and risk assessment of microplastics in the environment. Current studies, however, portray a wide spread in results on the occurrence of microplastic ingestion, highlighting a lack of comparability of results which might be attributed to a lack of standardisation of methods. We critically review and evaluate recent microplastic ingestion studies in aquatic biota, propose a quality assessment method for such studies, and apply the assessment method to the reviewed studies. The quality assessment method uses ten criteria: Sampling method and strategy, Sample size, Sample processing and storage, Laboratory preparation, Clean air conditions, Negative controls, Positive controls, Target component, Sample (pre-)treatment, and Polymer identification. The results of this quality assessment show a dire need for stricter quality assurance in microplastic ingestion studies. On average studies score 8.0 out of 20 points for ‘completeness of information’, and ‘zero’ for ‘reliability’. Alongside the assessment method, a standardised protocol for detecting microplastic in biota samples incorporating these criteria is provided.