| SIIS | Sapporo Institute for International Solidarity 
| Others |
| SIIS | Silicone Implant Incompatibility Syndrome
| Others |
| SIIS | State Industrial Insurance System
| Others |
| SIIS | Storage Interface Interactions Specification
| Others |
| SIIS | Subsea Instrumentation Interface Standardisation
| Others |
| SIIS | Summer Institute for International Students
| Others |
| SIIS | Summer Institute for Israel Studies
| Others |
| SIIS | Systems and Internet Infrastructure Security
| Others |