Abstract: The invention relates to a flame-retardant methacrylic composition based on a methacrylic polymer comprising, per 100 parts of methacrylic polymer, from 15 to 25 parts, advantageously from 17 to 25 parts, preferably from 17 to 23 parts, more preferentially still from 19 to 22 parts, of at least one flame-retardant agent of formula (I) or (II): in which: R1 and R2 denote linear or branched C1-C6 alkyl groups and/or aryl groups; R3 denotes a linear or branched C1-C10 alkylene group, a C6-C10 arylene group, an alkylarylene group or an arylalkylene group; M denotes Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na or K; m is an integer between 1 and 4; n is an integer between 1 and 4; x is an integer between 1 and 4.