The sub-surface flow path through the Postojnska jama cave system has been monitored with 7 stations distributed along the flow path, monitoring stage and temperature. We have used the stage data to model flow through the cave system with the program package SWMM, simulating the active parts of Postojnska jama with simplified geometry. From the comparison of stage observations and predictions, we identified key sections in the cave, which control the sub-surface flow, such as passage constrictions, sumps and by-passes. Using a formal inverse procedure, we determined the geometry of this key sections by fitting predicted to observed stages, and we achieved a very high degree of correlation. Key words: modelling, hydrology, Postojnska jama. Modeliranje toka podzemeljske Pivke v Postojnski jami, Slovenija Z avtomatskimi merilniki in registratorji podatkov smo spremljali podzemni tok Pivke v Postojnski jami na sedmih točkah med ponorom in odtočnim sifonom v Pivki jami. Podatke nivojev in pretoka smo obravnavali z modelom EPA SWMM, s katerim smo simulirali tok v poenostavljeni geometriji kanalov. S primerjavo med opazovanji in modelskimi rezultati smo določili ključne odseke (podore, zožitve, sifone, obtoke), ki najbolj vplivajo na dinamiko toka podzemne Pivke. Glavne parametre teh odsekov smo določili z inverzno metodo, ki temelji na algoritmu soseske (Neighbourhood algorithm, NA) in pri tem dobili odlično ujemanje med modelom in podatki. Ključne besede: modeliranje, hidrologija, Postojnska jama.