Kotzig (see Bendy and Murty, Graph Theory with Applications, North-Holland, Amsterdam, 1976) conjectured that there exists no graph with the property that every pair of vertices is connected by a unique path of length k, k > 2. Kotzig (Graph Theory and Related Topics, Academic Press, New York, 1979, pp. 358-367) has proved this conjecture for 2 < k < 9. Xing and Hu (Discrete Math. 135 (1994) 387-393) have proved it for k > 11. Here we prove this conjecture for the remaining cases k = 9, 10, 11. (C) 2000 Elsevier Science B.V. All rights reserved.