To evaluate the short term safety and potential therapeutic effect of allogenic adipose tissue-derived stromal/stem cells (ASCs) + cholecalciferol in patients with recent-onset T1D. Prospective, phase II, open trial, pilot study in which patients with recent onset T1D received ASCs (1 × 10 cells/kg) and cholecalciferol 2000 UI/day for 3 months (group 1) and were compared to controls with standard insulin therapy (group 2). Adverse events, C-peptide (CP), insulin dose, HbA1c, time in range (TIR), glucose variability (continuous glucose monitoring) and frequency of CD4 FoxP3+ T-cells (flow cytometry) were evaluated at baseline (T0) and after 3 months (T3). 13 patients were included (8: group 1; 5: group 2). Their mean age and disease duration were 26.7 ± 6.1 years and 2.9 ± 1.05 months. Adverse events were transient headache ( = 8), mild local reactions ( = 7), tachycardia ( = 4), abdominal cramps ( = 1), thrombophlebitis ( = 4), mild floaters ( = 2), central retinal vein occlusion ( = 1, complete resolution). At T3, group 1 had lower insulin requirement (0.22 ± 0.17 vs. 0.61±0.26IU/Kg; = 0.01) and HbA1c (6.47 ± 0.86 vs. 7.48 ± 0.52%; = 0.03) than group 2. In group 1, 2 patients became insulin free (for 4 and 8 weeks) and all were in honeymoon at T3 (vs. none in group 2; = 0.01). CP variations did not differ between groups (-4.6 ± 29.1% vs. +2.3 ± 59.65%; = 0.83). Allogenic ASCs + cholecalciferol without immunosuppression was associated with stability of CP and unanticipated mild transient adverse events in patients with recent onset T1D. NCT03920397.