Wash the potatoes thoroughly and cook in plenty of boiling salted water for about 15 minutes. Mix yoghurt, horseradish, sugar and vinegar. Season with salt and pepper.
Clean and peel the cucumber and slice it lengthwise into strips. Drain potatoes, quench, peel and slice. Pluck salmon roughly. Wash dill, shake dry, pluck little flags from the stalks and chop coarsely.
Mix all prepared ingredients. Season with salt and pepper and serve.