Basement membrane abnormalities have often been observed in the kidney cysts of polycystic kidney disease (PKD) patients and animal models. There is abnormal deposition of extracellular matrix molecules, including laminin-α3,β3,2 (laminin-332), in human autosomal dominant PKD (ADPKD). Knockdown of PKD1 paralogs in zebrafish leads to dysregulated synthesis of the extracellular matrix, suggesting that altered basement membrane assembly may be a primary defect in ADPKD. In this study, we demonstrate that laminin-332 is aberrantly expressed in cysts and precystic tubules of human autosomal recessive (ARPKD) kidneys as well as in the kidneys of PCK rats, an orthologous ARPKD model. There was aberrant expression of laminin 2 as early as postnatal (PN) day 2 and elevated laminin-332 protein in PN day 30, coinciding with the formation and early growth of renal cysts in PCK kidneys. We also show that a kidney cell line derived from orpk mice, another model of ARPKD, exhibited abnormal lumen-deficient and multi-lumen structures in matrigel culture. These cells had increased proliferation rates and altered expression levels of laminin-332 compared to their rescued counterparts. A function-blocking polyclonal antibody to laminin-332 significantly inhibited their abnormal proliferation rates and rescued their aberrant phenotype in matrigel culture. Furthermore, abnormal laminin-332 expression in cysts originating from collecting ducts and proximal tubules as well as in precystic tubules was observed in a human end-stage ADPKD kidney. Our results suggest that abnormal expression of laminin-332 contributes to aberrant proliferation of cyst epithelial cells and cyst growth in genetic forms of PKD.