Dermatopathology is interesting field when a mathematical approach through the algorithm is followed. This chapter covers clues and pitfalls in diagnostic dermatopathology. Thickened stratum corneum to more than 1/3rd of the total thickness of epidermis is referred to as hyperkeratosis. Retention of nuclei in stratum corneum is parakeratosis, which indicates delayed maturation process and altered keratinization. Cornoid lamellation is kertain investigation of the epidermis at an angle from the center of which arises a parakeratotic column. Gross hyperplasia of epidermis, with elongated dermal papillae pushing up the epidermis, in the form of finger like process is papillomatosis. Church spires, acantholysis, dyskeratosis, dermal polymorphonuclear infiltrate, epidermal eosinophilic infiltrates, dermal eosinophilic infiltrate, foam cells, clues to early diagnosis of mycosis fungoides, extravasated RBCs, keratinocyte pallor, etc. are also covered in this chapter.