In 2018, a PRRS monitoring program started in Belgium. In this perspective, in Wallonia, where only 6% of Belgian pigs are kept, PRRS seroprevalence was assessed on both breeding and fattening pig farms. Serum samples (n = 1786 from 585 sows and 1201 piglets and/or growing pigs) collected in 2016 were tested with Elisa Idexx PRRS X3 on a maximum of 10 breeding and/or 5 feeder pigs per farm (i.e. 106 farrow-to-feeder/finish and 203 growing/finishing farms). An individual result was considered negative if the S:P ratio was < 0.4; a herd was considered positive if at least one pig had an S:P ratio ≥ 0.4. A survey addressed to these 309 Walloon pig owners gave 121 usable answers from 75/106 sow and 46/203 pig(let) owners. Overall, in farrow-to-feeder/finish farms, the apparent herd, individual and intra-herd prevalence were respectively 35% (95% c.i.: 26-43%), 36% (95% c.i.: 33-39%) and 38% (95% c.i.: 35-41%). In growing/finishing farms, the apparent herd, individual and intra-herd prevalence were respectively 60% (95% c.i.: 53-67%), 54% (95% c.i.:51-58%) and 85% (95% c.i.: 82-88%). This study showed that approximately 2/3 of Walloon breeding farms appear to be PRRS free. The next step will be to identify risk and protective factors from the survey. In the perspective of starting a national PRRS control program, these indicative results, even though they need to be confirmed, will be helpful in making specific regional decisions.