The paper highlights the importance of tubular lesions of the solitary kidney (SK), identified and monitored by means of urinary biomarkers, mainly N-acetyl-beta-D-glucosaminidase (NAG), albumin, alpha 1-, and beta 2-microglobulin. It is considered that the assessment of a SK should be performed with four and not three parameters as it was usually done until recently: renal function, proteinuria and blood pressure (BP), to which biomarkers should be added. The solitary kidney can result after nephrectomy for kidney transplantation. In some countries living kidney donors represent the only option for performing kidney transplantation. The SK in living donors has generally a good evolution, although sometimes renal injury manifested by proteinuria, arterial hypertension (AH), or diminution of renal function does occur. Therefore, living donors require attentive monitoring. The SK is considered to have a good evolution (even in donors), in spite of alterations of the above-mentioned clinical and biological parameters. The very infrequent cases who evolve progressively towards renal failure are not predictable, which requires monitoring of all persons with a SK. The SK represents a special situation in case of association with a disease affecting the kidney, such as urinary tract infection (UTI), diabetes mellitus, or systemic lupus erythematosus (SLE). Pregnancy occurring in a person with a SK also needs attentive follow-up. Pregnancy associated diseases, such as preeclampsia occurring in patients with a SK, impose appropriate therapeutic behaviour. The SK remains a particular entity in nephrology which needs to be carefully monitored.