Background <p>Hypertension and left ventricular (LV) hypertrophy (LVH) are common in autosomal recessive polycystic kidney disease (ARPKD). We examined clinical determinants of LV mass in children with ARPKD.</p> Methods <p>Retrospective study of patients with ARPKD with available echocardiogram data. Casual blood pressure (BP) percentiles, 24-h ambulatory BP monitor (ABPM) parameters, antihypertensive medications, and estimated glomerular filtration rate (eGFR) within 6&#xa0;months of echocardiogram were collected. Outcomes included LV mass Z-score, LV mass index [LVMI in g/m^2.7 and g/(m^2.16 + 0.09)], and LVH.</p> Results <p>Thirty patients with ARPKD (median age 7.2&#xa0;years [IQR 3.4, 12.8]) had echocardiograms, 28 had casual BPs, 11 had ABPMs, and 93% were on antihypertensives. LVH occurred in 23% based on LVMI in g/m^2.7 &gt; 95th percentile, and in 50% based on LVMI &gt; 45&#xa0;g/(m^2.16 + 0.09). Younger age correlated with higher number of antihypertensives (<i>ρ</i> = −&#xa0;0.46, <i>P</i> = 0.014) and higher casual systolic and diastolic BP percentiles (<i>r</i> = −&#xa0;0.74, <i>P</i> &lt; 0.001; <i>r</i> = −&#xa0;0.81, <i>P</i> &lt; 0.001). After adjusting for age, sex, and eGFR, LV mass was not significantly associated with casual BP or ABPM, except for a negative association between LV mass Z-score and casual diastolic BP percentile (β coefficient −&#xa0;0.31, <i>P</i> = 0.04). After adjusting for age, sex, and casual BP, both LVMI [in g/m^2.7 and g/(m^2.16 + 0.09)] and LV mass Z-score were significantly negatively associated with eGFR (β –1.08, <i>P</i> = 0.003; β –0.79, <i>P</i> = 0.007; and β -0.07, <i>P</i> = 0.01, respectively).</p> Conclusions <p>Young children with ARPKD have a higher burden of hypertension. LV mass was unexpectedly not significantly associated with BP but was negatively associated with eGFR.</p> Graphical abstract <p></p>