A modular lavatory monument assembly configured to be positioned in the interior of an aircraft. The modular lavatory monument assembly includes first, second, third and fourth walls that cooperate to form an outer shell that defines a lavatory interior. The fourth wall includes an alcove extending outwardly therefrom. The assembly also includes a sink module positioned in the alcove, a mirror module positioned above the sink module in the alcove, and a door positioned on one of the second or third walls.