Context: The kinetics of prostate specific antigen (PSA) are generally assumed to be indicative of tumour progression and are therefore used in clinical decision-making in men on active surveillance for early prostate cancer. Objective: This review aims to provide support for exploiting PSA kinetics in an active surveillance setting. Evidence acquisition: We searched the Medline database and reviewed the evidence on both the relation between PSA kinetics before radical treatment for prostate cancer and outcome, as well as the role of PSA kinetics during active surveillance. Furthermore, the benefits and setbacks of different derivatives of PSA kinetics, minimum required time interval and number of measurements, practical recommendations, and pitfalls of their use in clinical practice are discussed. Evidence synthesis: The evidence concerning the prognostic value of the PSA velocity (PSA-V) and PSA doubling time (PSA-DT) is sparse, especially in active surveillance. PSA kinetics should therefore be combined with other diagnostic measures as the trigger for deferred radical treatment or repeat prostate biopsies. There seems to be consensus among several reports on the unfavourable outcome relating to a PSA-DT < 3-4 yr and on the favourable prognostic value of a PSA-DT > 10yr or a decreasing PSA level. online tools provide help with calculations and insight on disease development. The best method of calculation, number of measurements, and time interval between measurements is unknown for now. Conclusions: Despite the current deficits in our understanding of the natural behaviour of early prostate cancer and its relation to serum PSA levels, and despite several secondary factors playing a role in PSA kinetics, PSA kinetics are a practical parameter we can offer men on active surveillance to assess the status of their disease. (C) 2008 European Association of Urology. Published by Elsevier B.V. All rights reserved.