An x87 fused multiply-add (FMA) instruction in the instruction set of an x86 architecture microprocessor is disclosed. The FMA instruction implicitly specifies the two factor operands as the top two operands of the x87 FPU register stack and explicitly specifies the third addend operand as a third x87 FPU register stack register. The microprocessor multiplies the first two operands and adds the product to the third operand to generate a result. The result is stored into the third register and the first two operands are popped off the stack. In an alternate embodiment, the third operand is also implicitly specified as being stored in the register that is two registers below the top of stack register; the result is also stored therein. The instruction opcode value is in the x87 opcode range.