Background: In autosomal dominant polycystic kidney disease (ADPKD), obtaining measured total kidney volume (mTKV) by magnetic resonance (MR) imaging and manual tracing is time consuming. Two alternative MR imaging methods have recently been proposed to estimate TKV (eTKV(ellipsoid) and eTKV(PANK)), which require less time. Study Design: Cross-sectional and longitudinal diagnostic test study. Setting & Participants: Patients with ADPKD with a wide range of kidney function and an approved T2-weighted MR image obtained at the University Medical Centers of Groningen, Leiden, Nijmegen, and Rotterdam, the Netherlands, in 2007 to 2014. Test set for assessing reproducibility, n = 10; cohort for cross-sectional analyses, n = 220; and cohort for longitudinal analyses, n = 48. Index Tests: Average times for eTKV(ellipsoid) and eTKV(PANK) were 5 and 15 minutes, respectively. Bias is defined as (mTKV - eTKV)/mTKV x 100%; precision, as one standard deviation of bias. Reference Tests: mTKV using manual tracing to calculate the area within kidney boundaries times slice thickness. Average time for mTKV was 55 minutes. Results: In the test set, intra- and intercoefficients of variation for mTKV, eTKV(ellipsoid), and eTKV(PANK) were 1.8% and 2.3%, 3.9% and 6.3%, and 3.0% and 3.4%, respectively. In cross-sectional analysis, baseline mTKV, eTKV(ellipsoid), and eTKV(PANK) were 1.96 (IQR, 1.28-2.82), 1.93 (IQR, 1.25-2.82), and 1.81 (IQR, 1.17-2.62) L, respectively. In cross-sectional analysis, bias was 0.02% +/- 3.2%, 1.4% +/- 9.2%, and 4.6% +/- 7.6% for repeat mTKV, eTKV(ellipsoid), and eTKV(PANK), respectively. In longitudinal analysis, no significant differences were observed between percentage change in mTKV (16.7% +/- 17.1%) and percentage change in eTKV(ellipsoid) (19.3% 6 16.1%) and eTKV(PANK) (17.8% +/- 16.1%) over 3 years. Limitations: Results for follow-up data should be interpreted with caution because of the limited number of patients. Conclusions: Both methods for eTKV perform relatively well compared to mTKV and can detect change in TKV over time. Because eTKV(ellipsoid) requires less time than eTKV(PANK), we suggest that this method may be preferable in clinical care. (C) 2015 by the National Kidney Foundation, Inc.