Coccidiosis is an enteric disease caused by protozoa, especially Cystoisospora suis which can lead to large losses in production. Its transmission occurs through different routes, mainly affecting piglets in the first weeks of life and normally progressing with diarrhea unresponsive to antibiotic therapy. The objective of this work was to evaluate, in two seasons of the year, the occurrence of C. suis in piglets and sows, the transmission routes and source of infection and the influence of the preventive use of toltrazuril on these epidemiological parameters. Two experiments were carried out, the first being in winter; under the influence of prophylactic use of toltrazuril; and the second in the summer, six months after the suspension of the prophylactic use of toltrazuril. The study included 36 sows (18 controls, 18 treated toltrazuril). The following samples were collected: rest of the sows, water from the individual drinkers in each cage, organic swabs present in the keepers' shoes, environmental swabs pre and housing, present in the cages in the rooms and accumulations of the maternity cage. As were disclosed to coproparaological and PCR exams. The presence of C. bebe ocysts is the winter and summer control following samples: sow feces (2.84%) of the winter and summer control groups (7.60%) of the winter and summer treated groups and the treated group winter and summer, rectal swabs from litters (9.03%) in the control and treated groups in winter, collected from the environment (20.22%) from all groups. Like others, they were negative for the presence of the parasite. There was no difference between the control and toltrazuril groups and no positive samples were observed in the summer. The possible route of transmission of the agent in the present work was the water from the douros. Preventive therapy with toltrazuril in farms with low infection pressure is not necessary to control C. suis.