Background: Intracavernous injection (ICI) of adipose-derived stem cells (ADSCs) has been demonstrated promising for neurogenic erectile dysfunction (ED). However, due to the sponge-like structure of corpus cavernosum (CC) with abundant vessels, ICI was indeed like intravenous injection. Thus, the cell escaping may be a concern of safety and limited therapy, but the issue has not been clearly demonstrated yet. Methods: Suspensions of free ADSCs (FAs) and ADSCs-based spheroids (ASs) with suitable size were intracavernously injected at doses of 0.5, 1, 2, or 4 million cells. The cell loss and safety after ICI, erectile function and histopathologic change, etc. were analyzed with multimodality of methods. Findings: Most FAs escaped from sponge-like CC after ICI due to their small size, weakening stem-cell therapeutic efficacy. Worse still, the escaped cells were shown to cause widespread pulmonary embolism (PE), and even death in some animals. Further, it was founded that the therapeutic effect of FAs may be ascribed to the larger cell clusters which spontaneously aggregated before ICI and were trapped within CC after ICI. In comparison, cell loss and PE were significantly avoided by transplanting ASs. Importantly, better therapeutic outcomes were detected after ICI of ASs when compared to FAs with the same cell number. Interpretation: Transplantation of size-specific ASs instead of single-cell suspension of FAs for neurogenic ED may be a wiser choice to achieve steady therapeutic outcome and to reduce risks for the future clinical application. (C) 2020 The Author(s). Published by Elsevier B.V.