The business form assembly includes an integrated mailer and return envelope comprising first, second, third and fourth plies having first, second, third and fourth edges. The first and third edges of the four plies are adhesively secured one to the other. Additional lines of adhesive are inset from a tear strip containing the adhesive securing the first, second, third and fourth plies to one another for securing the second and third plies to one another. The second and third plies are inset along second and fourth edges to enable adhesive securement of the first and fourth plies along the first and fourth edges to one another. A return envelope flap is formed by a fold line in the third ply. A registering line of perforations in the second ply defines the back face of the return envelope and a record-keeping portion between the line of perforations and the fourth edge. Upon detachment of that record-keeping portion and insertion of it, together with other materials, in the return envelope, the return envelope may be returned to the sender. Thus, the mailer with return inserts may be formed solely of four plies. A fifth ply is used as a fly sheet.