Purpose Single positive core in a prostate biopsy is usually associated with indolent prostate cancer (PCa) and is one of the active surveillance (AS) inclusion criteria. We investigated whether single positive core PCa at biopsy could define an archetype of low-risk disease. Materials and Methods A total of 1320 consecutive patients were enrolled. Among them, 249 patients with single positive core PCa were followed up, and the clinical and pathological parameters influencing prognosis were analyzed. Results Out of the 249 patients, 172 (69.0%) had pathological findings ≥ pT2c and 87 (34.9%) had an undergraded Gleason Score (GS) based on the biopsy. Positive surgical margins (PSMs), extraprostatic extension (EPE) and seminal vesicle invasion (SVI) were found in 20.8%, 10.0% and 6.0% of patients, respectively. In a comparative analysis, we found that the PSA level, prostate weight and number of cores at biopsy are essential to correctly predict an indolent PCa. A total of 125 patients (67.3%) with nonpalpable tumors became high-risk tumors (pT2c-T3). Analyzing only nonpalpable tumors with a GS of 6 at biopsy (156 patients), we noted that 106 (67.9% of cT1) progressed from cT1c to pT2c-pT3. Conclusions Single core PCa have clinically significant disease in the Radical Prostatectomy specimens, with considerable rates of overgrading for the GS, pT2c-pT3, PSMs, EPE and SVI. The treatment plan must be evaluated individually for patients with single core PCa and must take into account other prognostic factors when determining whether a patient should be managed with AS.