Monolithic silica aerogels are nanostructured solids characterized with exceptionally high porosity and specific surface area. Although their strength can be improved by surface treatment with polymers, none of them has been tested yet as a filler in biocompatible polymer composites. The new aerogel–poly(methyl methacrylate) composites were prepared by free radical bulk polymerization of neat methyl methacrylate in the presence of natural and functionalized silica aerogels at 60°C, using cumene hydroperoxide initiator and 4,N,N‐trimethyl‐aniline redox pair. Synthetic conditions were set to be most similar to the setting of orthopedic bone cements. Structures, compositions, and molecular weight distributions were determined by scanning electron microscopy, combustion analysis, and gel permeation chromatography, respectively. Compressive strength, Shore D hardness and Gardner's impact strength were measured, and the fracture properties were compared to the matrices. All four aerogel fillers resulted in significant enhancement in compressive strength, reaching a maximum value of 123 MPa. Dissolution of H103PC‐1 natural and H106PB‐1 C16 modified aerogel containing specimens in simulated body fluid occurred in 20 days, leaving porous surfaces behind, which may give rise to higher tissue adhesion potential in bone cements. Heat treated silica aerogel in H112PA‐1 showed no leaching out, and its composites might be usefull in high‐load technical applications. POLYM. COMPOS., 36:348–358, 2015. © 2014 Society of Plastics Engineers