In free-range chicken production, animals long contact with the outdoor environment leads to their exposure to a large sort of gastrointestinal parasites, namely coccidia, whose prevalence in flocks is influenced by biotic and abiotic factors. The current national pioneer long-term survey aimed to assess Eimeria spp. oocysts prevalence and faecal shedding in a traditional Portuguese free-range chicken farm, on different production conditions. A total of 350 faecal samples were harvested in a free-range chicken farm located in North-western Lisbon district, Portugal, during the 2018-2019 period, being assessed four different groups of animals in the fattening phase. Quantitative and qualitative coprological techniques were performed to quantify Eimeria spp. prevalence and faecal shedding level. Coccidia prevalence was higher in groups studied in Summer and Autumn (72% and 80%, respectively), although oocysts faecal shedding levels were higher in the Autumn and Winter groups (1191 and 1562 Oocysts Per Gram (OPG)). Animals showed clinical signs of coccidiosis during the survey, especially in Autumn’s 1st sampling, with 42% of the faecal samples having blood. The lack of sanitary depopulations, length of the fattening phase (1 month), short pre-patent period of coccidia, exposure to different environmental conditions and irregular drug treatments with amprolium, were key factors responsible for the different parasitic scenarios observed during this survey.