‘One good turn deserves another’ is a proverbial expression that means, when someone does you a good turn, a good turn done in return is appropriate.

The proverbial expression ‘one good turn deserves another’ has been in the language since at least 1636, as here in William Camden’s Remaines concerning Britaine:

“One good turne asketh another.”

‘One good turn deserves another’ is in use in colloquial English but is also a legal concept in the area of trade or exchange of goods or services. A contract is said to be binding if it is ‘One good turn deserves another’, that is, if it involves an exchange of goods or services for something of comparable value, usually money.

The proverb is often used to describe corrupt practise, where favours (notably political or sexual favours) are illicitly given in exchange for cash. that is, ‘you scratch my back and I’ll scratch yours’.

One good turn deserves another.A little wordplay involving the synonyms ‘turn’ and ‘tern’ was used by the scriptwriters of the 1991 thriller movie ‘The Silence of the Lambs’, starring Jodie Foster and Anthony Hopkins as Clarice Starling and Dr. Hannibal Lecter:

Hannibal Lecter: Plum Island Animal Disease Research Center. Sounds charming.
Clarice Starling: That’s only part of the island. There’s a very, very nice beach. Terns nest there. There’s beautiful…
Hannibal Lecter: Terns? If I help you, Clarice, it will be “turns” for us too. I tell you things, you tell me things. Not about this case, though. About yourself. One good turn deserves another. Yes or no?