1. Using a sharp knife, carefully cut away all the peel and pith from the grapefruit and oranges.
2. Working over a bowl to catch the juice, carefully cut the grapefruit and orange segments between the membranes to obtain skinless segments of fruit. Discard any pips. Add the segments to the bowl and gently mix together. Cover and let chill until required or divide between 4 serving dishes and serve at once.