The infestation of boring polychaetes can represent a serious problem for mollusks in natural populations and aquaculture. In the Mexican Pacific, their effects have been scarcely studied. So, this research aimed to analyze the infestation levels of Polydora sp. on Nodipecten subnodosus in the Ojo de Liebre Lagoon. Between May 2014 and October 2015, 639 specimens from four banks were collected to examine the spatial and temporal variations of the number of blisters by valve and their relationships with the scallop size. Around the lagoon mouth, the smaller scallops (<51 cm2) dominated, having the higher infestation percentages: Chocolatero: 88 ind (61%), Zacatoso: 86 ind (51%). In contrast, the larger scallops (51-89 cm2) were found in the inner lagoon, with smaller percentages of infestation: La Concha: 35 ind (21%) and El Datil: 29 ind (19%). The right valves, in closer contact with the bottom, were more infested than the left; those from Chocolatero and Zacatoso had more blisters (right 51-61%, left 14-15%), whereas in La Concha and El Datil both valves had fewer blisters (right 19-21%, left 6-8%). Larger scallops (51-89 cm2) from La Concha had low (5 ind) and medium (4 ind) infestation levels, and those smaller from Chocolatero (13-51 cm2) had high levels (34 ind). However, the relationship size scallop-infestation level needed to be clarified since larger scallops of El Datil also had high infestation levels (6 ind), and smaller specimens of Zacatoso showed lower (25 ind) and medium (27 ind) levels.