The picture shows the disrobing room in a ladies' public bath in ancient Rome, a subject which gave the artist ample opportunity to display both his archaeological knowledge and his skill at painting marble. Niches for holding clothes and valuables are seen on the right, while in the middle-distance women are being led by slaves to the tipidarium for massage. It has been suggested that the main figure was modelled by the artist's elder daughter Laurence, who was twenty-one at the time, but it seems more likely that the sitter was her step-mother, Alma-Tadema's second wife, born Laura Epps. Compare her husband's portrait of her of 1880, entitled Interrupted (Swanson, op.cit., 1990, no.257, repr. p.399), and the later likeness in A Family Group of 1896 (Swanson, no.375, repr. p.459). The figure in An Apodyterium has remarkably similar features, as well as the red hair that was characteristic of Laura's family.

The picture had a rapturous reception when it appeared at the Royal Academy in 1886. It was voted the 'picture of the year' by readers of the Pall Mall Gazette (Sargent's Vickers Sisters being considered the worst exhibit), and every critic seems to have agreed. The Art Journal described it as 'painted with all the artist's unerring precision and skill; nothing could be more dainty than the nude figure of the girl stooping to fasten her sandal, or the group of damsels in the background.' The Times called it 'Mr Alma-Tadema's little masterpiece ... when we come before the "Apodyterium", and contrive to forget for a moment the indifferent work that surrounds it, we feel ourselves in the presence of a man who in his own department is really great.' Having commended the painting of the marble and the flesh, the writer concluded: 'the whole picture is composed with so much knowledge and finish, with such a unity of idea, and in so lovely a scheme of colour, that we must rank it among Mr Alma-Tadema's finest pictures of this size.'

The 'scheme of colour' also appealed strongly to F.G. Stephens, the art critic of the Athenaeum. 'Though it is comparatively small', he wrote, 'the picture which will attract most attention this year will ... be Mr Alma-Tadema's view of An Apodyterium of a Roman bath ... On our right, beside the bench, are two ladies, one of whom is in the act of fastening her girdle. Her abundant draperies fall about her and only half conceal her contours, while they emphasise her graceful movememts and the beautiful proportions of her figure. Fine as these are, their charm is enhanced by the wealth and harmony of the colours of her dress, which are chief features in the chromatic scheme of the picture, and help to bring out the pure rich brilliance of the carnations of the other figure, a nude brunette, who is stooping to tie the sage-green silk ribbons of her boot. These dark carnations are further enhanced by contrasting with the ... purple-brown garments on which the girl sits. A contrast of another sort is supplied by the soft yet splendid tint of the white marble pilaster which rises behind her. A second chamber, seen behind, serves as an anteroom to the bath. A group of girls are crossing it, and their figures are dispersed with great art. Students of design will enjoy the manner in which each damsel moves, as well as the perspective of the feet upon the floor. Beyond this chamber, which is in half-light, we have a view of the outer court of the bath, with its columns and Pompeian decorations in pure sunlight. Fine as are the colouration in general and the different colours of this picture, its draughtsmanship and drawing proper are equal to them in beauty and completeness.'

The picture continued to appeal even when Alma-Tadema was out of favour. Graham Reynolds, writing in 1966, felt that it showed the artist 'at his best, .... his finicky technique and his obsession with the fashionable lineaments of his epoch merge into a genuine comprehension of the past and a certain exquisite preciosity.'

A composition sketch and a drawing of the nude girl, the latter possibly made alter the picture rather than for it, are recorded in previous literature.