Uraemia is defined as an increased concentration of urine constituents in the blood (azotaemia) combined with the multiple systemic alterations that result from advanced stages of renal insufficiency. Primary renal disease prior to acute or chronic renal insufficiency is the most common cause of uraemia in dogs and cats. Therefore the following therapy recommendations focus on this pathogenesis of uraemia. The terms renal disease, renal insufficiency, azotaemia and uraemia will be explained in the beginning, as these are often used incorrectly. In this respect the aetiology, pathophysiology and signs of acute and chronic renal insufficiency will be differentiated. Additionally, important pharmacokinetic and pharmacotherapeutic aspects, which should be considered in the therapy plan, are elucidated. In contrast to the chronic form, the determination of the primary cause in acute renal insufficiency is sometimes possible. Relative to their treatment schemes the most important causes of primary renal damage are listed. In the second part of this article the symptomatic therapy of uraemia will be discussed in detail.