Put a large pot of water to boil on the stove.

In a small saucepan, combine sugar, water and salt over low heat until sugar is dissolved.

Add vinegar.

Take off heat and cool.

When water in big pot is boiling, drop whole cucumbers in. 

Boil for 5 minutes.

Remove from water, cool a bit, peel and slice.

Slice onion thin, (optional) to taste.

Place cucumbers in plastic containers, layer with onion.

Pour cooled sugar/vinegar mixture over the cucumbers to cover.

Place in your refrigerator, can be eaten in a couple of hours.