Are both breasts implanted at the same time?

Not necessarily: Typically in cases of cosmetic surgery yes but this is not necessary in cases of mastectomy or other problems.

Usually they are: Usuallynthey are implanted at the same time unless there is some reason to do one only such as a mastectomy, congenital asymmetry or deflation, etc.

Usually Yes.: If you are referring to the use of breast implants for elective breast surgery ( breast augmentation), both breasts are usually augmented at the same time. It is the unusual case where a breast implant is used on one side only ( for aesthetic surgery purposes). If the procedure is being performed for reconstruction purposes ( after breast cancer surgery), one-sided procedure is often indicated.