Externally the building's federation style features are relatively intact and its characteristics are as follows; essentially symmetrical facade; red brick with painted stone or stucco trim; enclosed verandahs to upper storey separated by an elaborate parapeted gable bearing the hospital name and the date of inception.

Enclosed verandah to the ground floor with late twentieth century aluminium framed glazing set in finely crafted brick arches.

[1] Internally the buildings components reveal two distinct phases of development ranging from the mid-late nineteenth century to the Federation period (formerly Alderley).

Its fabric both internally and externally remains essentially intact and characterised as follows; small scale symmetrical facade with a projecting bay window.

Ornate pressed metal ceilings, beam encasing and iron structural columns to ground floor.

[2][1] Parts of the original cottage known as "Alderley" occupied by the Hospital in 1885 remain buried below the present Administration building.

[3][1] Balmain Hospital - Main Building was listed on the New South Wales State Heritage Register on 2 April 1999 having satisfied the following criteria.

[1] In addition to the early 20th century development the building records a series of later alterations made to accommodate changing needs.

[3][1] The place is important in demonstrating aesthetic characteristics and/or a high degree of creative or technical achievement in New South Wales.

Its external visible fabric retains most of the original architectural details and character, with the exception of the slate roofs and the chimneys which were removed.

[3][1] Despite substantial changes in usage of some parts of the building, the majority of detailing and the spatial arrangements inspirited in the early 20th century have remained, enabling the interpretation of their original use to be made.