For over more than a decade, the progressive evolution of Peptide Receptor Radionuclide Therapy (PRRT) for the treatment of tumors expressing somatostatin receptors has been constantly challenging—and challenged by—dosimetry. The improvements reached in the therapeutical applications of 90Y- and 177Lu- radiolabeled peptides are considerable, and new perspectives are on the way. These results have been possible due to the special complicity among various disciplines having the optimization of PPRT as common goal, with dosimetry at center stage. Its role has been precious for an attentive radionuclide and radiopeptide selection, for the upgrading of the protocol rationales and therapy schemes, for toxicity prevention. Especially, the high irradiation of the kidneys, the low but inevitable dose to the bone marrow, as well as the large dose variability of non-target organs and tumors, which emerged from the clinical trials, have been sustaining the need of reliable dosimetry. Although dose estimates still do not reach the finest accuracy, relevant progress in dosimetric methods is being obtained. Their application to this quite early therapy—avid of information—addresses the examination of the risk-benefit balance, toward the approach of a tailored treatment planning. The availability of dosimetric data has allowed to evaluate the efficacy of renal protective agents and to validate radiobiological models for dose-toxicity correlations on kidneys. The probability of renal impairment being predictable, the injected activity can be fitted to any patient for a safe kidney dose.