PHP ima dva paralelna sustava za probleme: tradicionalne greške (upozorenja, obavijesti, fatalne greške) i iznimke (objektno-orijentirane, hvatljive sa try/catch). Moderni PHP ujedinjuje većinu toga pod Throwable hijerarhijom, a dobra praksa favorizira iznimke.
Tradicionalne razine greške
E_NOTICE → minor issues (e.g. using an undefined variable) — script continues
E_WARNING → non-fatal problems (e.g. include of a missing file) — continues
E_ERROR / Fatal → serious errors (e.g. calling an undefined function) — script HALTS
E_DEPRECATED → use of deprecated features
