In a kettle combine the potatoes with enough salted cold water to cover them by 2 inches, bring the water to a boil, and simmer the potatoes, removing the small ones as they are done, for 30 to 40 minutes, or until they are tender. Drain the potatoes and let them cool until they can be handled. Peel the potatoes and cut them into bite-sized pieces.
In a large bowl whisk together the vinegar and salt and pepper to taste, add the oil in a stream, whisking, and whisk the dressing until it is emulsified. Add the potatoes and the parsley and combine the salad well.
