Many people have a slight difference in the length of their legs. Researchers estimate that 40 to 70 percent of the population has one slightly shorter leg.
Whether a slight difference in leg length is a problem tends to depend on the individual. For example, in athletes, a small difference in leg length may make a big difference in performance. Similarly, in an elderly person with heart trouble, a small discrepancy may make a big difference in walking, since even a 3 cm limb-length difference has been shown to increase an elderly person's heart rate while walking.
You should talk to your doctor about your concerns. Your doctor is in the best position to determine any individual problems you may have.