The North Sea plaice, Pleuronectes platessa (Linnaeus, 1758), is a commonly studied commercial flatfish with poorly known ovarian histology. The following dataset is a collection of female plaice gonad images and their corresponding histological slides, collected during a complete season of the plaice’s reproduction cycle. Stereology was used to determine the percentage of different structures found throughout the ovaries. Inter-agent calibrations were accomplished in order to harmonize the stereological readings, and were based on a comprehensive reading protocol and histological lexicon that were specifically written for the plaice’s ovaries. The distribution and homogeneity of the different cell types found throughout the ovaries were also evaluated. This dataset can be used to automate the stereological reading process (through statistical learning methods for example) or to objectively determine the plaice’s maturity phase, and link that information to either macroscopic measurements or through image analysis of the full ovaries.