Let V denote the set of prime numbers, and let P (n) denote the largest prime factor of an integer n > 1. We show that, for every real number 32/17 < r) < (4 + 3\/2)/4, there exists a constant c(r\) > 1 such that for every integer a ^ 0, the set \p e V : p = P(q -a) for some prime q with p'has relative asymptotic density one in the set of all prime numbers. Moreover, in the range 2 < t) < (4 + 3\/2)/4, one can take c(r)) = 1 + e for any fixed e > 0. In particular, our results imply that for every real number 0.486 < # < 0.531, the relation P(q -a) x q" holds for infinitely many primes q. We use this result to derive a lower bound on the number of distinct prime divisors of the value of the Carmichael function taken on a product of shifted primes. Finally, we study iterates of the map q H> P(q -a) for a > 0, and show that for infinitely many primes , this map can be iterated at least (log log^) 1+o(1) times before it terminates.2000 Mathematics subject classification: primary 11N25, 11N64.