| S1 | Swimmers with very severe coordination problems in four limbs or have no use of their legs, trunk, hands and minimal use of their shoulders only. Usually only swim on their back. Swimmers in this class would usually be wheelchair bound and may be dependent on others for their every day needs. |
| S2 | Swimmer able to use their arms with no use of their hands, legs or trunk or have severe co-ordination problems in 4 limbs. |
| S3 | Swimmers with reasonable arm strokes but no use of their legs or trunk; swimmers with severe coordination problems in all limbs and swimmers with severe limb loss to four limbs. |
| S4 | Swimmers who use their arms and have minimal weakness in their hands but have no use of their trunk or legs; swimmers with coordination problems affecting all limbs but predominantly in the legs; swimmers with limb loss to 3 limbs. |
| S5 | Swimmers with full use of their arms and hands but no trunk or leg function; swimmers with coordination problems of all limbs. |
| S6 | Swimmers with full use of their arms and hands with some trunk control but no useful leg function; swimmers with coordination problems (usually these athletes walk); swimmers with major limb loss of 2 limbs on the same side; specific type of dwarfism (< 130cm for women and 137cm for men). The exceptions being the dwarfs who are found in class SB6. |
| S7 | Swimmers with full use of their arms and trunk with some leg function; coordination or weakness problems on the same side of the body; major limb loss of 2 limbs. |
| S8 | Swimmers with full use of their arms and trunk with some leg function; limb loss of 2 limbs; swimmers without the use of one arm. |
| S9 | Swimmers with severe weakness in one leg only; swimmers with very slight coordination problems; swimmers with one limb loss Unless there is an underlying medical condition usually all of these athletes will start out of the water. |
| S10 | Swimmers with very minimal weakness affecting the legs; swimmers with restriction of hip joint movement; swimmers with both feet deformed; swimmers with minor limb loss of part of a limb. |
| S11 | These swimmers are unable to see at all or have minimal light perception and are considered totally blind. They must wear blackened goggles if they swim in this class. They will also require someone to tap them when they are approaching a wall. |
| S12 | These swimmers can recognise the shape of a hand and have some ability to see. There is a large range of vision ability within this class. |
| S13 | Swimmers who are the most sighted but have a significant visual impairment. |
| S14 | Swimmers who have a recognised intellectual impairment according to international standards as recognised by the World Health Organization ie IQ testing of 75 and below. |
| S15 (SHI) | Hearing Impaired |