Protein loss in the urine may be due to pre-renal, or post-renal causes. Pre-renal causes include processes such as elevated plasma protein levels, hypertension, strenuous exercise, hyper- and hypothermia, venous congestion, fever, or seizures. Renal proteinuria may be due to tubular disease, which usually causes a mild proteinuria, or glomerular disease. Glomerular proteinuria occurs when the glomeruli become damaged and allow plasma proteins, usually large amounts of albumin, to leak into urine. If pre-renal causes have been eliminated and proteinuria exists along with an inactive urine sediment, then the proteinuria is likely due to a renal cause. Post-renal causes of proteinuria include lower urinary tract or genital disease, since inflammmatory exudates or blood proteins mix with the urine. This case report discusses a presumptive glomerular disease causing proteinuria in a dog, along with the clinical findings, potential differential diagnoses, diagnostics, prognosis, available treatments, and outcome.